US1534321A - Method of lining cells for electrolytic refining - Google Patents

Description

W. HQOPES METHOD OF LINING CELLS FOR ELECTROLYTIC REFINING April 21,- 1925.

Filed Dec. 21, 1922 M g W L gwuemtoz W/Lu/w [700/ 5 hi mm/a Patented Apr. 21, 1925.

UNITED STATES PATENT OFFICE.

WILLIAM HOOPES, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB T ALUMINUM COM- PANY OF AMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA.

METHOD OF LINING CELLS FOR ELECTROLYTIC REFINING.

Application filed December 21, 1922. Serial No. 608,288.

resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have in-' vented certain new and useful Improvements in Methods of Lining Cells for Electrolytic Refining, of which. the following is a full, clear, and exact description.

This invention relates to therefining of metals by electrolytic separation or removal thereof from alloys or mixtures containing other metals or substances, and pertains more particularly to the provision of a thermally and electrically insulating lining for the cell or pot in which the refining is effected. Tts chief object is to provide an effective method of forming a lining which can be used advantageously in processes or operations involving the high temperatures incident to the refining of aluminum with fused or molten electrolytes, as for example electrolytes containing cryolite in substan tial amounts. To this and other ends the invention comprises the novel features hereinafter described.

Of the various types of cells to which the invention can be applied I have selected for illustration and specific description herein theone which at the present time is considered most convenient and effective for use in refining aluminum alloy or impure alumlnum to obtain metallic aluminum of substantial purity or substantially devoid of metals or other substances which, although present in the alloy or impure metal, are not desired in the refined product. The cell referred to comprises a metal shell of cylindrical form with a closed bottom, preferably made of steel, to furnish the necessary mechanical strength. In some cases it may be advantageous to cover part or all of the shell outside with heat-insulating material. The shell is divided horizontally near its top into two sections electrically insuiated from each other, providing a relatively deeplower section and a correspondingly shallow upper section. Tnside of the lower section is a bottom-lining of refractory and elec trically conductive material, preferably carbon, and beneath the latter there may be a. layer of refractory heat-insulating material,

as powdered bauxite, alumina, magnesia, or fire-clay bricks, etc.,. to diminish or minimize loss of heat through the bottom of the cell. bove the carbon bottom lining, at the sides thereof, the shell is provided, by means of the present invention, with a refractory side-lining joined to the said bottom lining and extending over the joint between the two shell sections to a plane well up toward the top of the upper section. This side lining has good thermaland electrical insulating properties, and serves the important purpose of keeping the contents of the cell (when in use) from contact with either shell section and of lessening or minimizing the escape of heat through the sides of the cell above the carbon bottom. Being electrically non-conductive, or having very high specific resistance, the side lining does not impair the electrical separation of the shell sections although covering and closing the joint or space between the two. Around its upper portion the shell may be provided with cooling means, preferably a water jacket made in two parts, one above and one below the joint between the shell sections. This may serve either or both of two purposes: to foiint-he aforesaid side lining by freezing in close adherence to the inner surface a fused material (or mixture of materials), and to prevent undue heating of the outer portion of the side lining at the high temperatures that may be encountered when.

the cell is in use.

The apparatus outlined above is illustrated in the accompanying drawings, in which I Fig. 1 is a plan View of the cell;

Figs. 2 and 3 are cross sections on lines 2-2 and 3-3, respectively, of Fig. 1;

Figs. 4 and 5 are detail cross sections on lines 4.& and 55, respectively, of Fig. 1, illustrating the water connections to and from and between the water jackets.

Fig. 6 is a detail cross section on line 6-6 of Fig. 1, showing the method of connecting the upper electrodes to the negative busbars.

Fig. '7 is a detail cross section on the same plane as Fig. 2, illustrating the method of securing the upper and lower shell sections strength without connecting the two electrical y.

The lower shell or shell section 10' is preferably made of steel in the form of a cyllndrical vessel of considerably greater diameter than height, and at or near its top 1t s provided with awater jacket 11 which 1s most conveniently formed by providing at the upper edge of the shell section an outwardly extending flange 12 of suitable width, and a flaring or conical ring l2 welded or otherwise hermetically joined to the underside of the flange and to the body of the shell below.

Above the lower shell section 10 1s an upper shell section 13 which may also be of.

steel and formed with hollow walls to provide an upperwater jacket 14:. The inner surface of the upper shell section is preferably flaring, as indicated. 0 To keep the sections electrically insulated or separated from each other a flat ring or gasket 15, of asbestos or other suitable material, may be used between-the two.

In order to give the shell structure sufficient mechanical strength the sections may be secured together by means of machine studs 16 passing upwardly through the flange 12 and threaded into pads 17 welded on the bottom'of the upper shell inside the water jacket. To prevent electrical connection the holes in the flange 12,- through which the studs pass, may have insulating bushings 18, and insulating washers 19 may be used.- If the water jackets are used, as in most cases they will be, the bushings and washers will not be subjected to a high temperature and hence they can be made of practically any insulating material which will not soften at temperatures below 100 C. and which can withstand the crushing stress exerted by the studs.

Suitable water connectionsfor the water jacketsare provided, and for the sake of simplicity and convenience these connections may be so constructed and arranged that the water flows through the two jackets in succession, preferably through the lower jacket first, For this purpose thejacket 11 may be provided at the bottom with an inlet nipple 20 connected by a pipe 21 to any convenient source of water, not shown, and at the to (to prevent pocketing of air) with an outlet nipple 22 connected by a pipe 23 to the inlet nipple24 by which water from the lower jacket is led into the bottom of the upper. The latter is equipped with an outlet nipple 25 (at the top to prevent air pocketing) which may be connected to a waste pipe 26 by means of a pipe 27. To avoid electrical grounding the pipes 21 and 27 may consist of rubber hose, as may also be the pipe 23 to keep the two shell sections electrically separate. The water used when the jackets are connected should be of suflicient purity to weasel prevent flow of current from one shell section to the other at the voltage'employed in operation.

In the bottom of the lower shell section a layer 28 of heat-insulating material may be provided, as powdered bauxite, alumina, magnesia, or refractory bricks, to decrease or minimize loss of heat through the bottom of the cell, and above this layer is a bottom lining 29 of refractory electrically conducting material, preferably carbon, and preferably having a cavity or depression in its upper portion shaped to form a bowl-like receptacle to receive the alloy or other material to be refined, as shown. The bottom lining can be conveniently and satisfactorily made by tamping into the shell a mixture of tar, pitch and granular or powdered coke, at a temperature high enough to make the mass plastic, and placing the shell and contents in an oven in which the temperature is gradually raised, say to about 600 C., for the purpose of baking andsolidifying the carbonaceous mass.

Good electrical connection may be provided between the shell and its bottom lining by means of metal collector plates 31, welded to the inner surface of the shell so as to be electrically and mechanically continuous therewith. These plates extend inwardly into the bottom lining, which is molded around them. At the plane of the collector plates the shell may be provided on the out side with metal contact pads 32, preferably Welded to the shell so as to be mechanically and electrically continuous therewith, to which padsbusses or busbars of copper, aluminumv or other suitable metal may be bolted tightly in place. The busbars may be in the form of long fiat plates 33 embracing the lower shell section, with their ends brought out at one side of the cell vfor convement connection to one terminal of a suit able source (not shown) of continuous or unldirectional current. In the refining opera t1on these busses are connected to the positlve terminal or pole of the source, so that the current enters the cell at' the bottom. he carbon bottom or bottom-lining, 29, constitutes what may for convenience be termed the lower. electrode of the cell.

he upper electrode may be multiple, as it were, composed of a suitable number of short thick rods 34 of refractory conductlng material, as for example carbon, but preferably graphite, arranged vertically and having'copper or other metal rods 35 threaded or otherwise-suitably secured in the tops of the electrodes. These metal rods serve to support the graphite cylinders or upper electrodes and convey current to or from the same, and for this purpose they mag be releasably and adjustably secured, as y means of clamps 36, to metal busbars 37 extending horizontally across the cell.

For convenience of access to the electrodes for adjustment, replacement, etc., the busbars may be' arranged at two or more different levels, as indicated, and may be supported on and secui'ed to a plurality of legs 38 to form a rigid framework. The latter may rest on the upper shell section, in which case they should be insulated from the shell section, as by any convenient and suitable means, not shown, if it is desired to have the upper shell section electrically neutral while the side lining, described below, is being formed by the method set forth hereinafter.

It is recognized that, strictly speaking, the aluminum layer floating on the bath and the layer of alloy underlying the bath, are the upper and lower electrodes, respectively, but these layers are termed herein. the cathode and the anode, and hence it is deemed permissible as well as convenient to refer to the graphite cylinders and the carbon bottom-lining, or their equivalents, as the upper and lower electrodes.

Metal or other molten material may be withdrawn from the upper portion of the cell through a tapping notch 39, which may be closed by means of any suitable refractory material (as for example bath material) which will not contaminate the cell contents with which it comes in contact. Molten metal or other material may be withdrawn from the lower part of the cell through a port or tapping hole 40, normally closed by means of a plug of dense charcoal or other suitable material.

On the inside of the cell is the side-lining, extending upwardly from the carbon bottom 29, over the joint between the shell sections and well up toward or even over the top of the upper shell section. This sidelining should be both thermally and electrically insulating, to decrease or minimize the conduction of heat to the water jackets as well as to prevent by-passing of current around any part of the cell contents undergoing electrolytic treatment in the refining operation. The lining should also be chemically unobjectionable and refractory enough to remain solidat the temperatures to which it is subjected in the electrolytic operation. Under these conditions a lining composed of or formed from mixtures containing metal fluorids as hereinafter more fully described, has been found highly satisfactory in practice.

A side-lining having the desired properties can be made by my present invention in the following manner, using mixtures of the kind referred to above.

The upper electrodes (which for this purpose may be composed of amorphous carbon) are lowered into contact with the carbon bottom and alternating current is passed through the cell by way of the upper-and lower electrodes, resulting in generation of heat at the points of contact. Powdered or granular fluorid mixture is deposited in the cell, and after a suflicient quantity has been melted the upper electrodes are raised so that the current is compelled to pass through the fused bath to the carbon bottom lining 29, and more bath material is supplied until the cell is filled to the desired height, the upper electrodes being raised accordingly. In the meantime water 1s being circulated through the water jackets.

Under such conditions there 'is formed on the cooled portions of the shell sections by freezing of the bath thereon a closely adherent crust which has good thermal and electrical insulating properties. Nor is the crust attacked in any substantial degree by fused fluorids subsequently used as electrolyte in the apparatus. In forming the crust it is sometimes difficult to prevent the admixture with it of more or less finely divided carbon, which would tend to render it conductive even when cold, and it is therefore important, in forming the crust, to exercise care to maintain the bath, from which the crust is formed, free from carbon and finely divided metal which would have the effect of rendering the crust conductive at the time of formation. Covering the carbon bottom of the cell with a layer of metal as soon as possible in order to minimize the amount of carbon exposed, aids in maintaining the bath in a carbon-free condition. It will be observed that in the process of forming the lining crustthe upper shell 13 is electrically neutral, because it is insulated or electrically separated from all other parts of the apparatus. In fusing the crust material the current flows between the upper electrodes 34 and the carbon bottom 29, the collector plates 31, lower shell section 10, and busbars 33, but not through the upper section 13. Keeping the upper section neutral during the formation of the side lining is an advantageous feature, as explained more fully hereinafter.

After the crust has been built up, the molten bath remaining may be dipped out, or drained out through the tap hole 40, and e the current cut off. Any residue of the bath material whichfreezes on the carbon bottom will ordinarily do no harm, so long as the entire bottom is not covered and insulated thereby, since it will be fused when the refining process is started and hence will be subsequent operation of the cell, asfor ex ample a mixture, containing aluminum, sodium and barium fluorids, the side-lining is preferably formed inthe following manner:

Bath material is melted in the carbon bottom, as above described, until the joint between the two cell sections is covered, and molten alloy of the kind which is to be used as the anode in the aluminum-refining process is poured into the cell in amount sufficient to form a layer of the desired depth. Being heavier than the bath, the alloy raises the latter to a higher level. More bath material is then supplied and the melting continued, until the shell is filled to the desired height. When the crust has been built up,by freezing on the cooled sides of the shell, and any treatment of the cell contents which may be necessary or desirable has been effected, the current is cut oif and'a portion of the molten bath dipped out to make room for a layer of molten aluminum, preferably the purest available, which is then poured on top of the remaining electrolyte or bath to serve as the cathode, it being understood, of course, that the bath is of greater density than the aluminum, so that the latter will float on the bath. There is thus established in the cell (which has been provided with a side-lining of high electrical and thermal resistance) a lower layer of alloy containing aluminum, a layer of electrolyte floating on the alloy, and an upper layer of aluminum floating on the electrolyte.

The refining process (using unidirectional current, of course) can now be begun, with the alloy as anode and the aluminum top metal as cathode, thecurrent being led'from the latter by the above described graphite cylinders dipping into it. When the desired amount of aluminum has been removed from the anode and added to the cathode, a portion of the top metal is removed through the opening 39. The impoverished anode alloy is then withdrawn through the tap hole 40, fresh anode alloy in the molten state be- .ing supplied in any convenient way, such that the refined metal floating on the bath will not be contaminated. This operation may be conveniently performed by means of a carbon funnel, which, after eing preheated, is let down until it nearly reaches the bottom of the cell, which has preferably been cut out of the circuit. The refined metal entrapped in the funnel may be dipped out with a hand ladle, after which fresh anode alloy is poured in. The funnel is then liftedout and the refining process is resumed. The-fresh anode alloy introduced is preferablvjsufficient in amount to raise the bath andtop'metal until the surface of the latter is atthe 'S'ame level as before the withdrawal. 51* f: a

The provision of a tapping opening, as

" the notch 39, isan advantageous feature,as

reenter it permits top metal to be removed without dipping it out, which is a laborious. method and is apt to contaminate the metal. Moreover, the upper tapping opening permits removal of the top metal automatically as fresh anode alloy is supplied to the cell, the top metal rising and flowing out at the same rate as the inflow of the anode alloy. The

cell is thus left in condition for immediate resumption of the refining operation when the proper amount of fresh alloy has been supplied.

The operation of melting down the electrolyte and forming the side-lining can be performed with unidirectional current if desired, in which case the current is passed from the upper electrodes to the lower, thus requiring that the cell connections be reversed when the refining operation begins. Alternating current is preferred, however, as it avoids the time and trouble involved in the reversal necessitated by the use of direct current. The side-lining or crust may be composed of or formed from any suitable material or materials which will not seriously contaminate the electrolyte or bath subsequently employed in refining and which will produce a crust having the desired insulating properties, preferably thermal as well as electrical. It has been found. that a mixture of cryolite (aluminum and sodium fluorids) with the addition of a fiuorid of higher freezing point, as for example calcium fluorid, gives a crust which stands up well. In that mixture the proportions of cryolite and fluorspar may be one to one.

The voltage and amperage needed to fuse the mixture employed in the crust formation depend largely upon the composition of the mixture and the quantity to be melted, the size of the cell and the effectiveness of its heat-insulation, etc., and hence it is lIIlPOSSlble to give definite figures which would be universally applicable. In practice the power input is regulated to roduce fusion of the materials used and maintain them at the desired temperature.

The anode alloy should be supplied in suflicient amount so that it will remain in an electrically continuous layer on the bottom of the cell throughout the refining operation. A bath layer of suflicient depth must be used so that the top metal will in no case come into contact with any portion of the side crust which has previously been covered by the anode alloy. It is evident that the changes in composition of the anode alloy, incident to the refining operation, cause corresponding changes in its volume and in the position of the up er and lower surfaces of the bath layer. referably the top metal layer is kept wholly within the upper shell section, and it is also highly desirable to.

have the upper s'hell section electrically insulated from all portions of the apparatus. That is, the upper shell section should be electrically neutral. This is advantageous for the following reasons.

If the upper shell section should become electrically positive, current would leak from it through any conducting regions that might exist in the boundary crust and would flow directly to the top metal, thus by-passing more or less of the current around the bath or electrolyte with consequent impairment of the efficiency of the cell. Moreover, although every precaution be taken to make the boundary crust or side-lining non-conductive when it is formed, it is in most cases difiicult to prevent it from being slightly conductive in one portion or another. Even though such portions are very poorly conductive in the beginning, some current will pass from the metal composing the upper shell section if that section is made positive, and the conductivity of such leakage paths will gradually increase, due to the deposition along them of metal taken from the shell by electrolytic action. This attack on the steel of the shell injures the latter and may eventually cause complete penetration of the water jacket. On the other hand, gradual breaking down of the resistance of the crust also takes place if the upper portion of the shell is connected with the negative terminal or otherwise becomes negative, probably because of deposition of metal along leakage paths due (apparently) to initial penetration of sodium vapo into the crust and subsequent substitution of aluminum for the sodium.

Accordingly it is preferred to have the upper section electrically neutral, but nevertheless advantage may be taken of a lining, made conducting in this or any other mannor, as a means for carrying current to the upper section as the negative terminal of the co Cooling of the shell by means of water has been found to be preferable, but air cooling may in some cases be permissible. The latter method, however, is less certain, espccially in the refining operation, because although a properly formed crust composed of material having the desired high specific resistance is non-conductive or nearly so when cold, it becomes conductive when hot. When air cooling is used, it may happen that heat penetrates the crust at certain portions, for various reasons, until the shell becomes heated in spots to a temperature at which the entire thickness of the crust at such points becomes conductive. This forms a comparatively low resistance path for current, after which the heating becomes cumulative, due to the passage of current accompanied by gradual increasing of the temperature of the section of crust through which the current flows. The more effective cooling obtained by the use of water prevents these hot spots in the crust from penetrating through to the shell, and it is therefore easier to maintain proper insulation by water cooling than by air cooling.

Having the top part of the shell electrie cally neutral, particularly during the crustforming stage, is also very advantageous. When this part of the shell is negative in the stage referred to, the crust during its formation is penetrated by sodium and the latter, by reaction with aluminum fluorid of the bath, is replaced by finely divided metallic aluminum, which if present in sufficient amount will seriously impair the electrical insulating properties of the crust. Hence, in order to prevent the boundary crust from being initially conductive it is important that little or no current be permitted to pass through'itduring its formation. On the other hand, when the upper part of the shell is positive in the crust formation the crust is likely to be penetrated by iron, with like disadvantageous results.

The cell described is not claimed herein as an apparatus but is claimed as such in my copending application Serial No. 608,287,

filed December 21, 1922. v

The use of graphite as material for the upper electrode or electrodes is not claimed herein but forms the subject of the copending application of Francis G. Frary, Serial No. 672,867, filed November 5, 1923.

It is to be understood that the invention is not limited to the features of appartus and procedure herein specifically illustrated and described but can be practised in other ways and with other devices without departure from its spirit.

I claim- 1. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising fusing by electrical energy in a metal shell and in contact with the shell surfaces to be lined, material having a suitable freezing point, and artificially cooling such surfaces to freeze thereon from the molten material a closely adherent crust; while maintaining in electrically neutral condition a portion of the said shell surfaces above an electrically separated lower portion.

2. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising v establishing in a metal shell composed of upper and lower sections, a molten body of material, of high specific resistance when in the solid state, sufficient in amount to bring its upper surface within the upper section of the shell; passing current through the molten material to maintain the same in a state of fusion; freezing from the molten material a (.rust on the shell surfaces with which the material is in contact; and maitnaining the upper section of the shell electrically neutral while said crust is being formed. l

- 3. In the artof forming an electrically insulating lining in an electrolytic cell, the improvement comprising establishing in a metal shell composed of upper and lower sections, a molten body of material, of high specific resistance when in the solid state, sufiicient in amount to bring its upper surface within the upper section of the shell; passing current through themolten material to maintain the same in a state of fusion; water-cooling the inner surface of the upper shell section to freeze from the molten material a crust on the inside of said upper shell section; and maintaining the said upper shell section electrically neutral while the crust is being formed.

4. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising establishing in a metal shell composed of upper and lower sections and having a carbon bottom lining in the lower section, a layer of molten material, of high specific resistance when cold, and underneath the same a molten metallic layer, said layers being of sufficient thickness to bring the upper surface of the upper layer within the upper shell section; passing current through the two layers to maintain at least the upper in the fused state; freezing from the upper layer a crust on the upper shell surface with which it is in contact; and maintaining the upper shell section electrically neutral while the crust is being formed.

5. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising establishing in a metal shell composed of upper and lower sections and having a carbon bottom lining in the lower section, a. layer of molten mixture containing aluminum and sodium fluoride and underneath said layer a molten metallic layer, the two layers being of sulficient thickness to bring the upper surface of the upper layer within the upper shell section; passing current through the two layers to maintain at least the upper in the fused state; freezing from the upper layer a crust on the upper shell surface with which it is in contact; and maintaining the upper shell section electrically neutral while the crust is being formed.

6. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising establishing in a metal shell composed of upper and lower sections, a molten mixture containing aluminum and sodium fiuorids, suflicient in amount to bring its upper surface within the upper section of the shell; passing current through the molten material to maintain the same in a state of fusion; freezing from the molten material a crust on the shell surfaces with which the material is in contact; and main-l weasel taining the upper section of the shell electrically neutral while said crust is being formed.

7. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising forming a carbon bottom-lining in the lower section of a metal shell composed of upper and lower sections and providing said carbon lining with a cavity in its upper surface; establishing wholly within the said cavity a molten metallic layer and on the latter a layer of molten material, of high specific resistance when cold, sufficient in depth to bring it into Contact with marginal portions of the carbon bottom-lining and the adjoining sidesurfaces of both sections of the shell; passing current through said layers to keep them molten; freezing from the molten upper layer a crust on the side and bottom surfaces with which the layer is in contact; and maintaining the upper shell section electrically neutral while the crust is being formed. 1

8. In the art of forming an electrically insulating lining in an electrolytic cell, the improvement comprising forming a carbon bottom-lining in the lower section of a metal shell composed of upper and lower sections and providing said carbon lining with a cavity in its upper surface; establishing wholly within thesaid cavity a molten metallic layer and on the latter a layer of molten mixture containing aluminum and sodium fluorids, sufficient in depth to bring it into contact with marginal portions of the carbon bottom-lining and the adjoining side-surfacesof both sections of the shell; passing current through said layers to keep them molten; freezing from the molten upper layer a crust on the side and bottom surfaces with which the layer is in contact; and maintaining the upper shell section electrically neutral while the crust is being formed.

9. In the art described, the improvement comprising establishing in the lower section of a metal shell composed of electrically separated upper and lower sections, a lower layer of molten aluminum alloy wholly within the lower section, and on the latter layer a floating layer of molten mixture containing aluminum and sodium fluoride in contact with the sides of both shell sections;

passing current through said layers to main- 1 tain the same in molten condition and freezing a crust from the upper layer upon the contiguous shell surfaces, while maintaining the upper shell section electrically neutral; establishing on the molten fluorid-containing mixture a layer ofmolten aluminum, as cathode, wholly within the crusted surfaces of the shell-section; and thereafter passing electrolyzing current through the three layers to remove aluminum from the anode and deposit aluminum on the cathode, while artificially cooling the crusted portion of the upper shell-section and maintaining the same electrically neutral.

10. In the art described, the improvement comprising establishing a layer of molten aluminum alloy in an electrically live lower section of a metal shell, and on said alloy a layer of molten electrolyte adapted to float on the alloy and extending into an electrically neutral upper section of the shell; water-cooling the shell to freeze an insulating crust from the electrolyte layer upon the contiguous surfaces of the shell-sections; establishing on the molten electrolyte a layer of molten aluminum wholly within the crusted surfaces of the upper shell-section; and-thereafter passing current between the lower layer of alloy and the upper layer of aluminum and thereby depositing aluminum from the former on the latter, while watercooling the shell and thereby preventing excessive heating of said crust.

11. In the art described, the improvement comprising freezing on the sides of a metal shell having an electrically neutral upper section and an electrically live lower section, from a fused bath contained in the cell and comprising a mixture containing aluminum and sodium fluoride, an electrically insulating crust or side-lining extending from within the live section upwardly into the upper neutral section; and thereafter passing current from a layer of molten aluminum alloy in the live section, through the fused bath, to a layer of molten aluminum lying wholly within the crusted sides of said electrically neutral section, whereby aluminum is removed from the alloy and is added to the molten aluminum at the top,

' while cooling the crusted sides of the upper shell-section to prevent excessive heating of I the crust therein.-

12. In the art described, the improvement comprising establishing a molten lower layer of aluminum alloy in an electrically live lower section of a metal shell having an electrically neutral upper section, and on the alloy layer a floating layer of molten electrolyte; water-cooling the shell and thereby freezing an insulating crust from the electrolyte upon the sides of the live and neutral sections of the shell; establishing in the crusted neutral section a layer of molten aluminum floating on the electrolyte; and passing current through the three molten layers to remove aluminum from the lower layer and deposit aluminum on the upper layer, while continuing to water-cool the shell and thereby prevent excessive heating of the said crust.

13. Themethod of forming a refractory non-conducting lining for an electrolytic cell, comprising establishing in a suitable shell a fused mass free from carbon and other conductive particles but containing the constituents designed to constitute the. lining, maintaining said mass in a fused condition by passing current ther'ethrough between the shell bottom and an electrode dipping into said mass while maintaining in electrically neutral condition portions of said shell on which a non-conducting lining is to be formed, and cooling shell portions on which a lining is desired, whereby asolid crust is formed from the materials of said mass.

14. The method of insulating from one another and from a contained bath two portions of a conducting shell of a cell for the electrolysis of fused salts which consists in separating contiguous portions of said shell by insiilating material; establishing therein across the joint between said portions a fused mass of normally non-conductive material free from carbon and other normally conducting material but containing material desired in said lining, and cooling said contiguous shell portions whereby a refractory substantially non-conducting crust is formed on said'shell across said joint, while maintaining one of said shell portions electrically neutral.

15. The method of insulating from one another two portions .of a conducting shell ofhn electrolytic cell which consists in separating contiguous portions of said shell by insulating material; cooling said shell portions and solidifying a refractory substantially non-conducting crust on said shell across the joint between saidjportions from a molten bat-h established therein, while maintaining one of said shell portions electrically neutral. v

16. The method of putting in operation an electrolytic cell for the electrolysis of fused salts having an electrically live lower section and an electrically neutral upper section,

which consists in establishing in said cell abody of fused salts, maintaining the fusion by passing a current through said fused salts and said electrically live lower section, while keeping the said upper section electrically neutral, freezing a side lining on said cell from said fused bath, and thereafter passing current from a layer of molten metal in said livesection through said fused bath to a suitable cathode while maintaining said side lining by continuously cooling it.

In testimony whereof 1 hereto afiix my signature.

WILLIAM HOOPES

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