US1534317A - Electrolytic production of aluminum - Google Patents

Description

Patented Apr. 2l, 1925.

UNITED STATES PATENT OFFICE.

WILLIAM HOOPES, F PITTSBURGH, AND FRANCIS C. PRABY AND JUNIUS D. ED-

WARDS, 0F OAXIONT, PENNSYLVANIA, ASSIGNOBB T0 ALUHINUH COMPANY 0F AMERICA, 0F PITTSBURGH, PENNSYLVANIA, A CORPORATION 0F PENNSYLVANIA.

ELECTRLYTIG PRODUCTION 0F ALUMINUI.

Application llled December 21, 1922. Serial No. 606,284.`

To all whwn it may concern:

Be it known that we, IVILLIAM Heeres, FRANCIS C. FRARY, and J UNlUs D. EDWARDS, all citizens of the United States of America,

5 the said VILLIAM Hoorns residing at Pittsburgh and the said F aimais C. Fiumi' aud JUNiUs D. EDwAims residing at Oakmont, all in the county of Allegheny and State of Pennsylvania., have invented certain new and useful Improvements in Electrolytic Production of Aluminum, of which the following is a full, clear, and exact descri tion.

This invention relates to the production of aluminum of substantially any desired high degree of purity, by the electrolytic refining of impure aluminum or aluminum-alloys colptaining other substances. Several methoi s for the purpose have been suggested in the past, but it is well known that none heretol'ore proposed has been capable of conimercial operation. In fact it has been widely held among those skilled in the production of aluminum that such processes are inherently impractical. Our invention is the result of ,extensive investigation und study of the problems involved, combined with prac-tical work on a large scale, and has been found to be thoroughly feasible. 'ith it we have produced' commercially, at

low cost, metal having a metallic aluminum content as high as 99.98 per cent.

In our method impure aluminum or aluminum alloy is used in a. molten state as anode, iu contact with a superimposed bath or elec- .ti-olyte, preferably consistin of or containing one or more fused fluori s, with or without the addition of chlorids; the pure aluminum being deposited on a cathode of molten aluminum, preferably floating-on the bath l0 or electrolyte. The invention embraces several advantageous features which, although capable of use separately, are especially ctlective when employed oonjointly. One of the most important of these is the provision of an alloy, for use as anode, which at the operating temperature will be sufficiently mobile to permit the aluminum contained in it to continually replace, at the surface of the anode alloy, aluminum removed there- 5 from by the electrolysis. Without such provision impurities in the alloy may be dissolved in the electrolyte and deposited at the cathode in such amount as te seriously affect the purit of the refined metal. Another feature o importance in our invention resides in promoting the secondary reactions by which impurities diolved from the anode alloy are ria-precipitated thereon and those deposited on the cathode are re-dissolved in (the bath; as for example b producin an energetic circulation where y the bath eely Washes, or is freely washed by, the wntiguous surfaces of the anode and cathode respectively. A further advantageous feature consists in maintaining at least a certain minimum proportion of aluminum in the anode alloy, as by withdrawnp,r more or less of the latter and supplying fresh alloy in its place, for the purpose' of preserving the selective aluminumdissolving action of the bath.

The electrolyte or bath which we prefer to employ in the present method contains aluminum iluorid, with the addition of one or more'fluorids of metals mori` electropositive than aluminum. Preferably the bath is of about the following composition:

ties, about 2 The addition of fluorids of other of the alkali or alkali-earth metals is permissible, but the presence of halogen anions other than those of lluorin is undesirable, and indeed is highly objectionable if aluminum of a high degree of purity is to be obtained; 0n the other hand, ther resence of oxygen anions is not usually obleetionable, and :iccordingly alumina may be an ingredient of the bath'. In some, cases alumina is a desirable ingredient, but not, in general, in amount suicient 'to saturate the mixture. The use of a bath containing between 20 and per cent of barium luorid, or strontium fluor-id in like amount, or a mixture of the two, is claimed broadly in our copendin application Serialv No. 608,285. Barium an strontium are alkali earth metals having atomic weights above 80.

Speaking generally, the bath or electrolyte A bath such as the above is fluid within the range of suitable working temperatures, and is of lower density than the impure aluminum or aluminum allo `which has been found in general most suitable for the process. Hence the bath will float on the molten alloy. At the same time the bath is of higher density tla the refined or pure aluminum, so that the latter will float on the former. Moreover, the'bath described is capable of dissolving a substantial amount of alumina. For a more extended discussion of electrolytes for the electrolytic relining of aluminum 'reference ma be had to the copendin application -o William Hoopes and rancis Cs Frary, Serial No. 608,286; and to our copendin ap lication, above mentioned, wherein t e e ectrolytc preferred for our present invention is claimed broadly.

In general, any alloy of aluminum may be refined which has a greater density than the bath or electrolyte and which will remain satisfactorily mobile while the refining rocess is going on. In case thefdensit o the `alloy is too low it may be raised by t e addition of a heavier metal or metals. Of the metals that may be used for such urpose copper has been found preferable. n practice the working temperature of the preferred bath lies between 850 and 1,100" C., approximately, with a preferred temperature of about 950 (3. A bath of the above analysis has at the preferred temperature lnentioned a density of between about V2.5 and 2.7 grams per cc. Aluminum at the same temperature has a density of about 2.3 grams r cc. and, if it containsonly small quantities of heavy metals or even considerable uantities of silicon or other impurities o low density, will oat'- on instead of sinking in the bath. The presence of about 25 r cent of copper gives an alloy mixture which at a temperature of 950 C. has a density of about 2.8. This is sulciently above the density of the bath to insure that the alloy will not float but will remain at the bottom. A greater proportion of cop er may be used, however, provided the al oy is satisfactorily mobile at the ugper limit of temperature for smooth wor ing, say between 1050 and 1100 C.-

The' freezin int of. pure copper 1s around 1083" hilt ,the addition of 2 pery cent of silicon reduces the freezing point to about 1050 C., and an alloy containin per cent of copper and 1B per cent of si icou num is extracted. 'Generally s ing point lowered from about 1050 C. to A about 930 C. by the addition of 5 r cent of silicon, and to about 795". C. by t e addition of 10 per cent of silicon.. The presence of silicon in amount between 2 per cent and 32 per cent of the copper-plus-silicon therefore prevents the allo from freezing at a temperature of 1050 or higher, and thus permits the removal of all or substantially -v all of the aluminum without causing the residual alloy to freeze at the temperature mentioned. The presence of iron and titanium, or either of them, tends to raise the freezing point, which is 'of course, obj actionable. t er materials than silicon will serve the purpose of preventing the freezing of the alloy as the aluminum is removed, but

silicon is preferred, and its cheapness permits it to be thrown awa slag when the residuaLal o `is afterwards treated for recovery of the copper. On the other hand, tin or other low-melting material miscible with aluminum and copper, would have to be thrown away, or would have to be recovered in the course of reclaiming the copper. In either case the net co'st of the process would be increased.

Aluminum has ofitself the capability of lowering the freezinpoint of co per, and Vadvantage may be ta en of this act, when necessary or desirable, by removing the alloy from the cell while it still contains some aluminum. In other words, the amount of aluminum and the amount of silicon should be so adjusted with respect to the other constituents that the anode alloy will at all timesremain mobile within a rurrge of working temperatures which `will not cause ob]ec Vtionable alteration of the bath as by vola tilizal'ion of one or another of its ingredients. Thus if it is desired to remove all of the aluminum, the silicon content when the aluminum has been removed should be not less than about 2 per cent of the copperplus-silicon; but if the silicon content is not of itself suflicient to maintain the desired mobility it may be necessary to remove the alloy (or re lace a portion of it with fresh metal, or adld silicon) before all the alumiaking there ought to be enough silicon to ee the alloy mo ile at a temperature of 1000 or thereabouts, when the aluminum content has been `reduced to the desired extent. Silicon to the form ofY Ctl Athe upper electrodes to the amount of per cent of the copper-plussilicon is ordinaril ample for the pur ose if the iron content is not more than a out 5 per cent. It is to be understood that it is not in all cases necessary to have the alloy completely molten. Under some circumstances the presence of a limited amount of solid high-freezing material entrained in the anode alloy is not objectionable so lon as it does not reduce the mobility of the aglloy nough to prevent its free circulation and For the above reasons, the anode alloy used is preferably one containing copper in amount above per cent, and silicon in amount betwcen 2 and 32 per cent of the copperplussilicon, approximately. One of the applications of our invention is for the recovery of aluminum from electrothermally produced aluniinum-copper alloys, as for example one of about the following eimposition:

`Fer een' Aluminum Copper Silicon T 10 Iron, less than 5 Titanium, less than 1 A convenient and practical method for producing an anode-alloy such as the above is described and claimed in our copending application Ser. No. 608,283, filed December 2l. 1922.

In the refining operation, unidirectional or continuous current from any suitable source is led into the anode alloy or impure aluminum and passes ,upward therefrom through the bath or electrolyte to the cathode above, with resulting deposition of aluminum thereat. High enough current density is used to make the resistance losses within the cell sufficient to maintain the working temperature.

Convenient and suitable apparatus for practiciingY the present invention is illustrated in the accompanying drawing, but it is to be understoml Iliat the invention is not limited thereto. The apparatus illustrated is claimed broadly in a copeiiding application of 'illiani Hoopes.

Referring to the drawing,

Fig. l is a plan view of the cell.

Figs. and 3 are cross sections on lines --2 and 3&3, respectively, of Fig. l.

lFigs. 4 and ."i are detail cross sectionson lines 4 4 and 5-5, respectively, of Fig. l, illustrating` the water loiinections to and from and between the water jackets.

Fig. ti is a detail cross section on line 6 6 of Fig. l., showing the method of connecting the negative bushars.

Fig 7 is a detail cross section on the same planear: Fig. 2, illustrating the method 0f securing the upper and lower shell sections together to give adequate mechanical strength without connecting the two electricaly.

Fig. 8 is a detail sectional view illustrating a suitable anode for use in deoxidizing the electrolyte. Fig. 9 is a detail section on the same plane as Fig. 2, showing the heat-insulating top-- crust above the cathode metal.

The lower shell or shell section 10 is preferably made of steel in the forni of a cylindrical vessel of considerably greater dialneter than height, and at or near its top it is provided with a water` jacket 11 which is inost 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 12 welded or otherwise hernictically joined to the underside of the llange and to the body of the shell below.

Above the lower shell section l() is an up` per shell section 13 which may also be of steel and formed with hollow walls to provide an upper water jacket 14. 'llie inner surface of thel upper shell section is |irefcrably flaring, as indicated. 'lo keep the sections electrically insulated or separated from each other a flat ringpr gasket 15, of ashestos or other suitable material, may be used between the two.

In order to give the shell structurisullicient mechanical strength .the sections may be secured together h incaiis of niacliinc studs 16 passing upwar ly through the flange 1L. and threaded into pads 17 welded on thc bottom of the upper shell inside the water jacket. 'Io prevent electrical connection thiI holes in the flange 12, through which thc studs pass, may have insulating bushings 1H and insulating washers lt) may be used. -lf the water jackets are used, as in most-cases they will he` the bushings and washers will not bc subjected to a high temperature and hence they can be inade of practically :in v insulating material which will not soften at temperatures below 100 C and which can witlist and the crushing stress exerted by tln` studs. Mica lnis been found suitable for the purpose.

Suitable water connections for thc water jackets are provided, and for the sake ol' simplicity and convenience these connections may be so constructed and arrang d that thc water flows through the two jackets in succession, preferably through the lower jacket lirst. ,For this purpose thc. jacket 11 may be provided at the bottoni with an inlet nipple 20 connected b v a pipe 2l to any convenient source of water, not shown, and at the top (to prevent pocketing of air) with an outlet nipple 29. connected by a pipe lit to the inlet nipple 24 by which water from the lower jacket is lcd into the bfittoni ol' thc upper. The latter is equipped with :in outllt) let 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 groundi the pipes 21 and 2 `mayyconsist of rubber ose, as may also tliepipe 23 to keep the two shell sections electrically separate. The water used when the jackets are connected should be of suicient purity to prevent the tlow of a substantial amount 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 owdered bauxite, alumina, magnesia, or re ractory'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 por ion to receive the alloy or other material to be refined. 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 placingx the shell and contents in an oven in whic the temperature is gradually raised, say to about 600 C., for thepurpose of baking and solidifyin the carbonaceous mass.

ood electrical connection may be provided between the shell and its bottom linii by means of metal, collector plates 3l, weld to the inner surface-of the shell so as to be electrically and kmechanically continuous therewith. These plates extend inwardly into the bottom lining, which is molded around them. At theplane of the 'collector plates the shell may be provided on the outside with metal contact pads 32, preferably welded to the shell so as to be mechanically and electrically continuous therewith, to which pads busses or busbars, of copper, aluminum or other suitable metal may be bolted tightly in place. The busbars may be in the form of long flat plates 33 embracing the lower shell section, with their ends brought out at one side of thc cell for convenient connection to one terminal of a suitable source (not shown) of continuous or unidirectional current. uring the refining operation these busses are connected to the^ positive terminal or pole4 of the sour-censo that the current enters the cell at the bottom. The carbon bottom 4or bottom-lining, 29, constitutes what may for convenience termed the lower electrode of the cell.

The upper electrode may. be multi le, com sed preferably of a suitable num r of s ort thick rods or cylinders 34 of graphite, arranged vertically and having co per or .other metal rods 35 threaded or ot erwise suitably secured to the tops of the elecbe Horstie Yon t trodes. These metal rods serve to support the graphite cylinders and convey current to or from the same, and for this purpose they may be releasably and adjustably sesured, as by means of clamps 36, to metal busbars 37 extending horizontally across the cell. For convenience of access to the electrodes, for adjustment, re lacement, ete., the busbars may be arrange at two or more diiferent levels, as in icated, and may be supported on and secured to a plurality of legs 38 to form a rigid framework. The latter may rest on the u er shell section, in which case it is preferable to have them insulated from the shell section, as by any convenient and suitable means, not shown.

It is recognized that, strictl speaking, the aluminum layer floati on t e 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 w l 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 ma be withdrawn from the/upper portion o the cell through a tapping notch 39 which may be closed b means of any suitable refracto material w Aich will not contaminate the ce l contents with which it comes in contact. Molten metal or other material ma;I be withdrawn from the lower part o the cell through a ortor tapping hole 40, normally close by means of a plug of dense charcoal or other suitable material.

On the inside' of the 45 ext/ending upwardly from ottom 29, over the joint between the shell sections and well up toward or evenover the top of the upr shell section. This sidelining should thermally and electrically insulating, to decrease or minimize the conduction of heat to the water'j ets as well as to prevent by-passing of current around any part of the cell contacts `undergoing clectrolytic treatment in the re ing operation. The lining should also chemically uiiobjectionable, and refractpry enough to remain solid at the temperatures to which it is subjected in the electrolytic relining operation. To meet these conditions a lininr composed of or formed from .a mixture o metal fluorids and alumina, as more fully explained in the ap lication of William Hoopes Juiiius D. dwa'rds and Basil T.

Y id, sei-iai No. 638,289, has been found hi hly satisfactory in practice. k

n the refining process the aluminum alloy or mixture of aluminum and other substances lies in molten form at the bottom of the cell as indicated at 46. Float' g on this is a layer 47 of fused bath or e ectrolyte, and

ie latter is a layer 48 of molten alumithe carbon b cell is a side-liningl the bath.

num, with the upper electrodes extending into it far enough to insure good electrical contract, say an inch or two. The molten layers may be established in the cell in any convenient manner, as for example by pouring the previously fused materials into place, using for the original aluminum layer the purest metal conveniently availableu The busbars 33 are connected to the positive terminal of the source of electrolyzingtunithe busbars 37 are directional) current, and

connected to the negative terminal of the same source. Any convenient and suitable means, not shown, may be employed to regulate the voltage and current supplied. Apparently the effect of the passage of the current is to set free liuorin or oxygen anions, or both, in Contact with the surface of the anode metal. The eti'ectof the liberation of these anions is to dissolve, from the anode alloy, aluminum and any impurity present in thealloy which is more electropositive than aluminum and to leave behind the im urities which are less electropositive. Any o the latter impurities which may be attacked by the anions tend to be immediately re-precipitated by a secondary reaction .between the aluminum, with which they are 1n contact, and the tiuorids or oxids of these ess electropositive metals, with the result that only aluminum and impurities which are more electropositive pass into solution in In the anode alloy described above there are no impurities which are more electro-positive than aluminum and practically only aluminum goes into solution so long as the aluminum content remains relatively high and the aforesaid secondary reactions can occur freely.

lVith a bath containing sodium and barium luorids there is also deposited at the cathode, along with the aluminum, some barium and solne sodium, the amounts being dependent to some extent at least upon theI current i in the bath, and the bath density used, and the quantitative composition of the bath. ,t has been found, however, that both barium and sodium react, at the working temperature, with aluminum iuorid to produce metallic aluminum and barium or sodium fluorid, as the case may be. Consequently so longas there is a sufficiently high proportion of aluminum fluorid can freely wash the bottom of the cathode metal layer, no barium is found in the lat-ter metal; but at the working temperature sodium, which is nearly insoluble in aluminum, is Set free in gaseous form and small proportions of it escape before the secondary reaction can completely redissolve all of it. Hence minuto traces of sodium are often found in the cathode met al, and some sodium escapes into the heat-insulating crust maintained above the top metal. This quantity, however` is usually very small when the bat-h is kept iu the proper condition of fusionand is not allowed to become deficient 1n aluminum lluorid.

Leadin electrolyzing current to the anode an from the cathode in such manner that a magnetic field is produced in the cell, is considered to be an advantageous feature. 'lhus in the apparatus illustrated the currents in the upper transverse horizontal busbars 37 and vertical electrodes 34, and in the lower encircling horizontal busses 33 and tapering horizontal distributor or collector lates 31, reduce in the cell a powerful an` non-uniform magnetic field having both vertical and horizontal components. On account of the relatively high specific resistance of the electrolyte, as compared with that of either the anode alloy or the. top metal layer, the current density throu hout the horizontal cross section of the electrol te and hence at its upper and lower sur aces, is substantially uniform. Likewise, the current density at tl1esurface of contact between the conducting bottom lining and the anode alloy (which latter has much better conductivity than the former) is substantially uniform, although the conducting plates or ribs in the bottom lining tend somewhat to concentrate the current. But inthe anode alloy the current flow may have horizontal as well as vertical components, due in part to the concentrating effect of the aforesaid plates in the bottom lining, and, probably more especially, to the bowl-like receptacle in the bottom lining, whereby some of the current can flow between the anode alloy and the conducting side Walls of the receptacle. These horizontal components of current- How in the alloy are largelyl radial in direction. The interaction of the current flowing in the anode alloy and the non-uniform magnetic field produced as explained above, causes the anode alloy (which, being molten, is in effect composed of movable conductors) to flow in various directions, and produces a powerful circulation and mixing of the ulloy. The stirring thus produced is, we believe, an important factor in replenishing the active surface of the anode alloy with aluminum fast enou rh to satisfy the anions set free thereat, ma :ing possible more extensive removal of aluminum from the alloy or the use of a higher current density, or both, without depositing impurities at the cathode in such amount as to seriously affect its quality. Moreover, the interaction of currents and magnetic field in the bath and in the cathode produces a like stirring effect in these layers which is advantageous in promoting homogeneity of composition and temperature and especially in preventing the bath from being impoverished of aluminum at the surface in contact with the cathode. 'lhc stirring etl'ect described also quate opportunity for the tions by which elements secondary reac- (other than alumiiiuni) deposited at the cathode are re-dissolved in the bath and by dissolved from thereon.

which impurities the anode are re-precip'itated As the refining operation proceeds, aluminum dissolved out of the anode alloy is deposited in molten form and when the desired has been deposited metal is removed anode metal is withdrawn hole 40, state` being supplied such that bath will not be tion ma means o ing preheated, is let bottom of preferably been cut out of refined metal entrappxed dl fte an a e,a .rwhic be di pcd out with a the resh anode metal is funnel is then liftpd out.

contaminated. be conveniently a carbon funnel, w

down until the cell, which has on the cathode,

amount of aluminum a portion of the top and the impoverished thro h the tap fresh anode metal 'in t e molten in any convenient way, the refined metal oatin 0n the This operal rformed by ich, after beit nearly the circuit. The the funnel may ou in. The ie fresh anode metal introduced is preferably sufficient in amount to raise the until the surface of the The tapping bath and top metal latter is at the before the withdrawal.

out and replenishing operations may be re eatedfrom time to time as necessary or interrupting the refining otherwise can Notwithstan capillary action at tween the liquid esirable without seriousl process, whic on continuously. ing the greater density of the bath, a portion of it is carried up the area of contact aluminum and the so lid boundary crust and rises to the surface of the former, where it s the weight of which is come the surface tension of prends in a thin layer,

insufficient to overthe liquid alumiiium. Consequently it spreads over the entire surface of the latter,

the escape of heat into the air,

a crust such there, forming for example, at 58, oii until the resulting crust that (the escape of heat bein its un er surface can the temperature of rise to the melting point this thickness saturated bath subsequentl and b y reason of solidiies as is indicated,

Fig. 9. This process goes thickens so muc thus retarded) the bath. When 'is attained, quantities of uny carried up by capillary action can accumulate in liquid form under the crust and finally grow to a mass of sufficient sink through the dimensions to aluminum.

be able to ence if the bath is kept unsaturated' with alumina the top after which crust forms up to a certain thickness,

its growth ceases. On the other hand if the freezing point of the bath is raised by allowing it to become saturated, liquid bath finding its way to the under-surface of the crust partially solidilies there and increases the thickness. This action would, if unchecked, result eventually iii bringing up a lar e portion of the bath from below the aluminum and causing it to attach itself to the top crust. At the same time, the boundary crust at the sides of the cell thickens in the same manner, and the net result would ultimately be more or less complete solidification of the bath unless its temperature is raised correspondingly. For these reasons it is desirable to keep the bath unsaturated in the normal operation of refinhe bath crust formed on the aluminum layer as above described serves as a convenient and goed heat insulating medium to minimize oss of heat from the top of the cell but it also entraps sodium as already explained, with consequent increase o alumina in the bath. The amount of sodium which thus escapes from the bath can be minimized by using in the latter the highest permissible amount of aluminum fluorid.

Instead of forming the heat-insulating top crust in the manner iereinbefore specifically described, such a crust mayy be produced by dusting over the up er sur ace of the aluminum la er,-soon a er it is put in place, a layer o finely divided alumina, carbon, ma nesia, or other suitable wdered materia This layer of finely divi ed material is rapidly cemented together by tlie liquid bath coming u from below and wetting it. The heat-insu ating property of the top crust may be increased by dusting any suita le powdered material over it after it has been formed, so that it is covered by a layer of such material, which is an excellent insulator by reason of its porous condition. Being su plied to the surface of the to crust after t e latter has solidified, the ad itional heat-insulating material is not cemented together and therefore retains its porosity. In

eneral, the best material for the purpose is bath which has been allowed to soli ify, since if any of it accident ally or incidentally finds its way below the top metal it does not contaminate the electrolyte.

Several methods are available for keeping the alumina content of the bath below the saturation point. For exam le, the to metal (aluminum) can be lad ed or tappe ortion of the saturated or nearly ath dipped out, liquid or solid alumina-free or deoxidized bath being added to take the place of that which was removed. The resulting mixture will then be well below the saturation point. 0r a portion of the crust can be broken away and removed, whereupon it will reform at the expense of the saturated bath within the cell,

4the excess alumina crystalliaing out in co- Hall process of i is illustrated in Figs. 1

rundum-like form. New alumina-free or deoxidized bath can be added either in solid or liquid form to take the place of that which went to form the new crust. In the first method the saturated bath removed from the cell can be regenerated and prepared for reentry into the process by crushing it and electrol zing it.

Anot er method of preventing saturation of the bath with alumina is to deoxidize the alumina continuously, or from time to time, in the refining cell itself, for example by electrolyzing the bath according to the producing aluminum from alumina. This may be accomplished by placing a carbon electrode in contact with the bath and connecting it with the positive terminal of the cell, thus making the carbon electrodeV an anode. Any current vleaving this carbon anode serves to electro] ze alumina in the usual manner, depositing aluminum on the cathode metal, or on the anode alloy, or on both, depending u on the voltage used; the oxygen being li erated at the carbon anode an forming CO2 with a portion of the carbon. The preferred way of using a carbon anode for the purpose and 8 of the drawings. p In these figures 50 represents a carbon disk into which is threaded a carbon stud 51, into the up er end of which is threaded a water-coo ed iron terminal 52. The latter is screwed into the bottom of a pipe 53 which serves to support the terminal and the disk and also to supply the electrolyzing current and the cooling Water. At its top the pipe is fitted into the underside of a closed chamber 54 through which a Water supply ipe 55 projects down into the pipe and wel to the bottom of the latter. Water thus introduced into contact with the iron terminal 52 rises around the pipe 55 and flows out of the chamber 54 by way of pipe 56. The pipe 53 is fastened on an insulated support 57 in such manner as to hold the carbon disk 50 submerged in the bath below the aluminum layer 48. 'Around the carbon stud 51, water-cooled terminal 52 and thelower end of pipe 53, is an insulating and refractory crust 58 which may consist of a mixture of bath and corundum previously cast in place. This crust serves to prevent the aluminum top metal from making contact with the carbon disk or with the electrically associated parts, and thereby prevents a short-circuit between the top metal and the deoxidizing anode. The latter can be electrically connected with the positive bus inauy convenient manner, preferabl through a suitable circuit-breaker, not s own, from which current may be carried by means of a cable 59 connected with the pipe 53. In practical operation it is usua ly sutlicient to deoxidize the bath intermittently, depending upon the rate (as determined by experience) at which oxygen finds its way into the bath. n

The energy-eliiciency in electrolytic processes of refining aluminum is dependent largely upon the perfection of the measures taken for preventing escape of heat. .'lheoretically a most no energy is required for the refinin but practically, in the absence of some oter adequate source of heat, suiiicient electrical energy must be expended to maintain the anode, the bath, and the cathode, in a fused condition, and consequently the amount of electrical energy which must be supplied is almost exactly the equivalent of the heat )ermitted to escape. After the heat insu ation of the cell has been perfected to the maximum practicable extent, nothing further can be accomplished in limitation of theanlount of heat escaping iven dimensions, and with the minimum ieat-loss the energ input required by the cell will also be a minimum. In the interests of power economy the cell should `be operated at the lowest practicable yoltage. Accordingly the electrolyte, which furnishes the major portion of the resistance. should be in as tlnn a layer as is permissible, and it has been found that a layer from 2.1/2 to 4 inches thick is in general satisfactory. With a bath or electrolyte of any predetermined workable depth, the current density permissible varies between af lower limit which is sufficient to maintain the anode, the bath and the cathode in afmolten state, and an upper limit at which "olatilization of the bath is excessive or at which too large a proportion of anode impurities go into solution. These limits. with the various bath-com ositions which have been found practicab e, are approximately 800 (l. and 1100o C., respectively, with a preferable working temperature of about 050 ("1. The permissible lower limit of current density also varies inversely with the dimensions of the cell, since the heut loss per unit ot' rolume in a large cell is lcss than that in u small cell on account of the smaller ratio of heat-dissipating area to the volume.

In a cell having a cross section through the electrolyte of 9.6 square feet it hasbecn found that the preferable current is, in general, 8500 amperes, but that the process is workable with currents between 7500 and 12000 amperes. The preferable current density in a cell having the electrolyte crossvsectional area mentioned is therefore 885 amperes per square foot, with a permissible minimum of about 780 ampere-s and a permissiblemaximum of about 1250 amperes, per square` foot. With the preferred current density mentioned, the total voltage between the terminals of the cell may be about (i volts. Larger cells may be operated with louter current densities and at lower voltfrom a heated body of,

llO

ages, and by varying the size of the cell, the composition of the bath, the conductivity of the bath, and the effectiveness of the heat insulation, the present electrolytic refining process is workable With current densities between about 50() and about 2500 am eres per square foot of cross section of the ath. In general the lower practicable limit of voltage is about 3.5 volts and the upper limit is of course indefinite.

rl`he layer of aluminum floating on the molten bath or electrolyte should be of suiiicieiit expanse to touch the boundary crust ot the cell around the entire perimeter thereof and should be thick enough to insure firm contact with this crust, in order to prevent or minimize volatilizatioii of the bath, which occurs to a great/er or less extent at working temperatures and increases as the temperature rises. On account of the surface tension of liiolteii aluminum the top layer should be ot substantial depth, and it is therefore desirable to maintain a thickness of at least 2, inches at all times.

So long as the aluminum content of the anode. alloy is not much below 10 per cent, by weight, no ditliculty is ordinarily experienced in obtaining a cathode metal having a purity adeipiate for commercial requirements. On tie other hand, as the anode alloy becomes impoverished of aluminum the selective action ot the bath becomes more and more impaired, impurities in the anode are dissolved in larger amount, and more and more of such im urities are deposited on the cathode. But y removing impoverished alloy and substituting fresh whenever the aluminum content has fallen too loW the major portion of the latter metal can be obtained in very pure form. The impoverished alloy can be disposed of in any advantageous manner, but for the purpose of making the copper re-iiseable the alloy may be sent to a copper refining furnace Where the major portion of'the remaining iron, titanium, and silicon may be removed by the common method of oxidation and slagring. ()i,in case these impurities are lovv, the alloy may be diluted with impure aluminum, such, for example, as is produced by the Hall process, and then returned to t-he cell. It molten impure aluminum be conveniently available, the impoverished alloy may be tapped into a criicible containing the desire amount of molten aluminum, thoroughly stirred, and promptly returned to the cell, so that the retiniiig operation pioreeds with the use of the saine copper.

It is to be understood that the invention is not limited to the specific procedure and apparatus herein illustrated and described but can be practiced in other ways without departure from its spirit.

lVe claiml. In the refining of aluminum, the steps composition of the allow comprising electrolyzin a molten bath with a molten allo as ano e containing aluminum materiali;Y in excess of the amount required to maintain the alloy mobile at a temperature too low to cause objectionable alteration of the bath, and depositing said excess aluminum in the molten state on a molten aluminum cathode in contact with said bath.

2. In the refining of aluminum, the steps comprising electrolyzin a molten bath with a molten aluminum a loy as anode compounded to remain mobile below a temperature causing material alteration of the bath, and depositing iii the molten state on a molten aluminum cathode in contact with said bath, aluminum removed electrolytically from the anode.

3. In the refining of aluminum, the steps comprising electrolyzing a molten bath with a molten aluminum alloy as anode containing silicon proportioned to cause said alloy to remain mobile below a temperature causing material alteration of the bath, and depositing in a molten state on a molten aluminum cathode the aluminum removed from said allo 4. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten aluminum alloy as anode containing silicon in amount adapted to maintain the allo in a mobile state regardless of its diminis iingaluminum content, and depositing the removed aluminum on a molten aluminum cathode through a molten bath.

5. In the refining of aluminum, the steps comprisin removing aluminum electrolytically rom a molten aluminum alloy as anode and depositing the aluminum upon a molten aluminum cathode through a molten bath, and controlling the bath and anode compositions to provide a common low temperature of mobility and maintain a definite relation of their densities.

6. In the refining of aluminum, the steps comprising electrolyzin a molten bath with a molten aluminum a loy as anode compounded to remain mobile below a tem rature causing material alteration of the girth, depositing said excess aluminum in the molten state on a molten aluminum cathode in contact with said bath, and correcting the from time to time to maintain its mobility.

7. In the refining of aluminum, the steps comprising electrolytically removing aluminum from a molten alloy thereof having a com osition enabling the alloy to remainmobile at the operating temperature and depositing the aluminum on a molten aluminum cathode tlirou h a molten bath capable of acting selective to dissolve aluminum from the alloy, andyby Withdrawal and replenishment of the alloy as it becomes im- Htl AIl() poverished maintaining an alloy composition adapted to preserve said selective action of the bath.

8. In the iefining of aluminum, the steps comprising electrolytically removing aluminumfrom a molten alloy thereof and deacting selectively to dissolve aluminum from the alloy, and maintaining the aluminum content of the alloy high enough to preserve said selective action of the bath.

9. In the refining of aluminum, the steps comprising electrolytically removing aluminum from a molten alloy thereof containing copper and silicon in proportions adapted to keep the alloy mobile during the electrolysis and depositing the aluminum on a molten aluminum cathode through a molten bath capable of acting selectively to dissolve aluminum from the alloy, and b Withdrawal and replenishment of the al oy as it becomes impoverished maintaining an alloy composition adapted to preserve said selective action.

10. In the refilling of aluminum, the steps comprising electrolytically removing aluminum from a molten alloy thereof containing copper and silicon in proportions adapted to keep the alloy mobile during the. electrolysis and depositing the aluminum on a molten aluminum cathode through a molten bath capable of acting selectively to dissolve aluminum from the alloy, while maintaining the aluminum content of the alloy high enough to preserve said selective action of the bath and maintaining a. current density and circulation of the bath, with respect to the contiguous anode surface, adapted to permit at said surface secondary reactions ade nate to prevent permanent solution of anode impurities in the electrol e.

11. In the refining of aluminum, the steps comprising electrolytically removing aluminum from a molten alloy thereof containing copper and silicnn in proportions adapted to keep the alloy mobile during the electrolysis and depositingr the aluminum on a molten aluminum cathode through a molten bath capable of acting selectivel to dissolve aluminum from the alloy; whi e maintaining an alloy composition, and a current density and circulation of the bath, with respect to the anode and cathode surfaces, adapted to permit at said surfaces secondary reactions adequate to precipitate, on the anode, impurities removed therefrom, and to revent permanent deposition `onthe cat ode, of bath components more electropositive than aluminum.

12. In the refining of aluminum, the steps comprising electrolytically removing aluminum from a molten alloy thereof as anode and depositin the aluminum on a molten aluminum catiode through a molten bath a molten 'main mobile,

capable of ,acting .selectively to dissolve aluminum from the alloy, while maintaining bath and alloy compositions, and an anode current-density and circulation, adapted to minimize removal of metals more electroncgative than aluminum from the allo and cause precipitation, on the alloy, o said more electronegative metals.

13. In the refining of aluminum, the steps comprising removing aluminum electrolytically from molten alloy thereof as anode and depositing the aluminum on a molten aluminum cathode through a suitable molten bath, and giving free plav to secondary reactions at the active sur aces of the anode and cathode, by maintaining intimate contact between the bath and the anode and cathode, maintaining active circulation of the bath and anode, and controlling the composition of the bath and anode and the current densities at the active surfaces thereof.

14. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten alloy thereof as anode and depositing the aluminum on a. `molten aluminum cathode through a suitableI molten bath, said anode alloy having a composition enabling-it to remain mobile below a temperature causing material volatilization of the bath; and giving free pla to secondary reactions at the active sur aces of the anode and cathode, by maintaining intimate contact between the bath and the anode and cathode, maintaining active circulation of the bath and anode, and controlling the composition of the bath and anode and the current densities at the active surfaces thereof.

15. In the refining comprising removing aluminum electrolytically from a molten alloy thereof as anode and depositing the aluminum on a molten aluminum cathode through a suitable molten bath compounded to Huid at a temperature below that of material volatilization, said alloy being compounded to remain mobile at a temperature below that of material volatilzation of the bath, and giving free play to secondary reactions at the active surfaces of the anode and cathode, b maintaining intimate contact between t e bath and the anode and cathode, maintaining active circulation of thebath and anode, and controlling the composition of the bath and anode and the current densities at the active surfaces thereof. a

v 16. In the refinin of aluminum, the steps comprisin the esta lishing in a suitable cell ath of fluoride containing aluminum iuorid, compounded to be fluid below the temperature of material volatilization of aluminum luorid; a molten anode of aluminum alloy to be refined, com unded to rewithin a wor ing range of aluminum content, below the temperature of material volatilization of the bath; and a of aluminum, the stepsmolten aluminum cathode; and passing electrolyzing current from the anode through the hath to the cathode in sutlicient quantity to maintain said anode, cathode, and bath in mobile condition and transfer aluminum from the anode to the cathode.

ll'. In the refining of aluminum` the steps comprising establishing in a suitable cell the gravitatively arranged -layersaamolten bath of fluorids containing aluminum lluorid. com pounded to have a density higher than that of molten aluminum and to be fluid below the temperature of material volatilization of aluminum fluorid, a molten anode ol' aluminum allov to lie refined. compounded to have a density higher than that of said bath and to remain mobile, within a working range ot aluminum content, below the temperature of material volatilization of the bath; and a molten aluminum cathode: and passing electrolyzing current from the anode through the bath to the cathode in sufficient quantity to maintain said elements in mobile condition and transt'er aluminum from the anode to the cathode.

18. In the refining of aluminum, the steps comprisingr removing aluminum electrolytically from a molten aluminum-copper alloy ot low iron and titanium content, as anode, containing silicon in such proportion to the copper as to maintain adequate mobility ot the alloy during the electrolysis; and depositing the aluminum so removed from a molten cathode.

l0. ln the refining of aluminum, the steps comprising removing aluminum electrolyticall)Y from a molten aluminum-copper alloy ot' low iron and t'tanium content, as anode, containing silicon in such proportion to the copper as to maintain adequate mobility of the alloy during the electrolysis, with a suitable electrolyte and a current density lictween 500 and 1.250 amperes, approximately, per square toot of cross sectional area of the eiectrolyte; and depositing thc aluminum so removed upon a molten aluminum cathode.

20. In the refining of aluminum, the steps comprising removing aluminum electrolvtically Jfrom a molten anode alloy containing, approximately, 30 per cent of aluminum, 55 per cent of copper, 10 per cent of silicon, less than 5 per cent of iron, and less than l per cent ot titanium, and depositing the aluminum so removed on a molten aluminum cathode.

Q1. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten anode alloy contain ing. approximately, 30 per cent of aluminum. 55 per cent of copper, 10 per cent of silicon. less than 5 per cent of iron, and less than l per cent of titanium, with a suitable electrolyte and a current density between 500 and 1250 amparos. approximately, per square foot of cross sectional area of the elec- `about 10000 C. and

trolyte; and depositing the aluminum so removed upon a molten aluminum cathode.

22. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten aluminum alloy containing copper in amount not less than about 20 per cent, and silicon in amounts between 2 and 32 per cent, approximately, of the copper-plus-silicon content, and depositing the aluminum so removed on a molten aluminuln cathode.

In the refining of aluminum, the steps comprising removingr aluminum electrolytically from a molten anode alloy of low iron and titanium content containing aluminum about 30 per cent, copper about 55 per cent. and silicon about 10 per cent, and depositing the aluminum so removed on a molten aluminum cathode.

Q4. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten anode alloy of low iron and titanium content containing aluminum, copper and silicon in proportions giving the alloy suitable mobility 0500 C., and depositing the aluminum so removed on a molten aluminum cathode.

25. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten alloy containing aluminum, copper, and silicon, in proportions giving the alloy suitable mobility below about 9500 C. and a density of not less than about 2.7 grams per cubic centimeter at the temperature named, aluminum so removed on a molten aluminum cathode.

20. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten aluminum-alloy containing copper and silicon in proportions giving the alloy suitable mobility below about 10000 C. when the aluminum content is reduced to the desired extent, and depositing the aluminum so removed on a molten aluminum cathode.

27. In the refining of aluminum, the steps comprising removing aluminum electrolytically from a molten aluminum-alloy containing silicon, copper, iron, and titanium, in proportions giving suitable mobility below about 10000 C. when the aluminum content is reduced to the desired extent, and depositing the aluminum so removed on a molten aluminum cathode.

28. In the refining of aluminum. the improvement comprising removing aluminum electrolytically from a molten aluminumalloy containing copper. silicon. iron, and titanium, in proportions giving the alloy, when the aluminum content is reduced to the desired extent. suitable mobility below a density not less than about 2.7 grams per cubic centimeter at the temperature mentioned, and depositing the below about and depositing the lfltl llll lill

l lyte aluminum vso removed on num cathode. o

29. In the electrolytic refining of aluminum, the steps comprising establishing va lower layer of molten `aluminum-alloy as anode containing copper and a li hter ingredient in proportions giving the a lo suitable mobility below 1100 C.and a ensity not less than'about 2.6 grams per cubic centimeter at the temperature mentioned, an up r layer of molten aluminum as cathode, an an intermediate layer of molten electrolyte com d ofa mixture containin fluorids of a uminum and sodium and tluorid of one or more alkali earth metals; and assing current between the anode alloy an the aluminum cathode and through the electrolyte; 'whereby' aluminum is removed from the anode ,and deposited on the cathode at a temperature below that mentioned.

30. In the electrolytic refining of aluminum., the steps comprising establishing a lower layer of molten aluminum-alloy as anode containing copper and a lighter ingredient in proportions giving the alloy a freezing int below 1100 C. and a density not less t an about 2.6 grams per cubic cen timeter at the temperature mentioned, an upper'layer of molten aluminum as cathode, and an intermediate layer of molten electrocompo'sed' of a mixture containing tluorids of aluminum and sodium and iluord of one or more alkali earth metals; and assiug current between the anode alloy an the aluminum cathode and throughthe electrolyte, with a current density between 500 and 1250 amperes, approximately, per square foot of cross sectional area of the electrol whereby aluminum is removed from t ie anode and deposited on, the cathode at a temperature below that mentioned.

3l.V In the electrolytc rening of aluminum. the improvement comprising establishing in downwardly successive layers a body of molten aluminum as cathode, a body fof molten electrolyte composed of a mixture containing aluminum, sodium, and barium tluorids, and a lower body of molten aluminum-alloy as anode containing copper and silicon in proportions ivin a density higher than that of the e ectro yte mixture and suitable mobilityl at a temperature not higher than about 1000 C?, and passing current through said layers in succession to remove aluminum from the lower layer and deposit it on the up r layer. t

-32. In the electro ytic refining of alumi-V num, the steps comprising establishing in downwardly successive la ers a body of molten aluminum as cat iode, a body of molten electrolyte comp of a mixture containing aluminum` sodium, and barium fluorids` and a body of molten alloy as anode containing aluminum about. 30 per cent,cop per about ."5 per rent, and silicon about 10 a molten alumiper cent; and passing current through. said ayers in succession to remove aluminum from the lower layer 'und deposit it on the upper layer.

33. In the electrolytic refining of aluniinum, the steps comprising establishing in downwardly successive layers a body of molten aluminum as cathode, a body of molten electrolyte composed of a mixture containing aluminum, sodium, and barium fluoride, and a o mo lloyus anode containing aluminum about 30 er cent, copper about r cent; and passing current through said ayers in succession witli a current density between 500 and 1250 amperes, approxi mately, r square foot of cross sectional area of t e electrolyte, to remove aluminum from the lower layer and deposit it on the upper layer.

34. In the electrolytic refining of alumi- 55 per cent, and silicon about 10 num, the steps comprising passing current through upwardly successive molten layers composed respectively of a body of ahumnum alloy, as anode, containingcoppcr and a lighter metal in proportions giving a density at least as high as about 2.7 grams per cu icv centimeter at a temperature of about 950 C.; a body of electrolytemixtiun containin aluminum, sodium, and barium uori s; and a body of molten aluminum as cathode; and by the passage of the current kmaintaining the materials in the molten state and in the la er formation described while simultaneously removing aluminum fromV the lower layerand depositing it ou the upper layer; and maintaining the alumina content of the electrolyte-mixturo below the point of saturation.

'35. In the electrolytic refining of aluminum, the steps comprising passing current through upwardly successive molten layers composed respectively of a body of aluminlim alloy, as anode` containing copper and a lighter metal in proportions giving a densit at least as high as about 2.7 grams per cu ic centimeter at a temperature of aboutl 950 C.; a body of electrolyte-niixture routaining aluminum, sodium, and barium f fiuorids; and a body of molten aluminum asV cathode: with a current density between 500 and 1250 ampei'es, approximately, per square foot of cross sectional area of the electrolyte; and by the passage o'f the cur,

- rent maintaining the materials in the molten state and .in the layer formation described while simultaneously removing aluminum from the lower layer and depositin it on the 4upper layergand maintainin t e alumina content of the electrolyte-mixture below the point of saturation.

36. In the electrolytic refining of aluminum, the stepsiconiprising establishing a lower hiver of .molten aluminum alloy, as

anode, containing copper and `silicon in prollfl portions giving a relatively high density and adequate mobility when the aluminum coutent is relatively low, an upper layer of molten aluminum as cathode, and an intermediate layer of molten electrol te composed of a mixture containing a uminum, sodium and barium fluorids in proportions giving a density between that o the anode alloy and that of the cathode aluminum when all are molten; establishing on the aluminum layer a heat-insulating top'crust composed, at least in part, of electrolyte coming up from below and freezing above the aluminum; passing current through the successive layers to remove aluminum from the anode and deposit it on the cathode; and treating the electrolyte to prevent saturation thereof with alumina and consequent thickening of the to crust.

37. In the electro ytic reining of alumi num, the steps comprising establishing a lower layer of molten aluminum alloy, as anode, containing vcop r and silicon in proportions giving a relatively higlh density and adequate mobility when tie a uminum con- ,tent is relatively low, an upper layer of molten aluminum as cathode, and an intermediate layer of molten electrol te composed of a mixture containing a uminum, sodium and barium .iluorids in proportions giving a density between that of the anode alloy and that of the cathode aluminum when all are molten; establishing on the aluminum layer a heat-insulating top-crust composed, at least in part, of electrolyte coming up from below and freezing above the aluminum; passing current with a density between 500 and 1250 amperes, approximately, met square foot of cross sectional area of t e electrolyte, through the successive layers to remove aluminum from the anode and deposit it on the cathode; and treating the electrolyte to prevent saturation thereof with alumina and consequent thickening of the to -crust.

3S. Tu the electro ytic refiningof aluminum, Ministeps comprising establishing a lower layer of molten alloy, as anode, -containing aluminum, cop r and silicon, on up er layer of molten a uminum as cathode, an an intermediate layer of molten electrolyte containing aluminum, sodium and barium fluoride; passing current through the layers in successionto remove aluminum from the lower and deposit it on the upper layer: and treatin the electrolyte at intervals to substantial y maintain the same unsaturated with alumina and thereby prevent excessive rise of the freezing point of the electrolyte.

39. In the electrolytic refini of aluminum the ste comprising esta lishing a 4lower ayer o molten aluminum alloy as anode containing copper and silicon in proportions giving a freezing point no higher than about 1050 C., an upper layer of molten aluminum as cathode, and an intermediate layer of molten electrolyte containing aluminum, sodium and barium iluorids; passing current through the said layers in succession to remove aluminum from the lower and deposit it on the upper iayer; and deoxidizing the electrolyte as necessary to prevent rise of its freezing point above substantially the' temperature mentioned.

40. In the eleetrolytic refining of aluminum, the steps comprising establishing a lower layer of molten alloy, as anode, containing aluminum about 30 per cent, copper about 55 per cent, silicon about 10 per cent, and containing less than about 5 per cent of iron and less than about 1 per cent of titanium; an upper layer of molten aluminum as cathode; and an intermediate layer of fluorid-electrolyte of intermediate density; passing current through said layers in succession to remove aluminum from the anode and deposit it on the cathode; and from time to time deoxidizing the electrolyte to reduce alumina therein and thereby prevent xceive rise of the freezing point of the electrolyte.

41. In the electrolytic refining of aluminum, the ste comprising establishing a lower layer o molten alloy, as anode, con-t taining aluminum about 30 per cent, copper about 55 per cent, silicon about 10 percent, and containing less than about 5 per cent of iron and less than about 1 er cent of titanium; an upper layer of mo ten aluminum as cathode; and an intermediate layer of iluorid-electrolyte of intermediate density; passing current through said `layers in succession to remove aluminum from the anode and deposit it on the cathode; from time to time deoxidizing the electrolyte to reduce alumina therein and thereby prevent excessive rise of the freezing point of the electrolyte; and maintaining the aluminum cathode layer sullicient in expanse to prevent excessive volatilization of the electrolyte.

42. An anode alloy of aluminum, containi suicient silicon to maintain adequate mo ilityl of the alloy as its aluminum content is dec in rening. 4

43. An anode-alloy containing aluminum, copper and silicon in proportions adapted to make the alloy adequately mobile below about 1050 C.

44. An aluminum-copper anode-alloy containing silicon in amount at least sufficient to keep the alloy ldequatel mobile at about 1050 C. when substantial y all the aluminum has been cted.

45. An aluminum anode-alloy containing copper and silicon in amounts adapted to. give the alloy a density not less than about 2.7 per cubic centimeter at a temperatum of approximately 10009 46. An alrminnm an e-alloy containing copper not less than about 20 per cent, and silicon between Qand 32 per cent, approximately,- of the copper-plus-silicon.

47. An anode-alloy containing aluminum, copper and silicon in proporiafons adapted to make the alloy adequately "mobile below about 105()o C., and having low iron and titanium content.

48. An aluminum anode-alloy containing copper and silicon in amounts adapted to give the alloy a. density not-less than about 2.7 grams per cubic centimeter at a, temperature of approximately 1000 C.. and having not more than about 5 per cent of iron and titanium.

49. An aluminum anode-alloy containing copper not less than about 20 per cent, and silicon between 2 and 32 per cent, ap toximately, of the copper-plus-Silioon, an having not more than about 5 per cent of iron and titanium.

In testimony whereof We hereto aix our signatures.

' WILLIAM HOOPES.

FRANCIS C. FRARY. JUNIUS D. EDWARDS.

copper not less than about 20 per cent, and silicon between 2 and 32 per cent, approxi mately; of tlie copper-plus-silicon.

47. An anode-alloy containing aluminum, copper and silicon in proportions adapted to make the alloy adequately 4mobile below about 10500 C., and having low iron and titanium content.

48. An aluminum anode-alloy containing copper and silicon in amounts adapted to give the alloy a density not-less than about 2.7 grams per cubic centimeter at a temperature ofV approximately 1000 C., and having ing not more than about 5 per cent of iron 90 and titanium.

In testimony whereof we hereto aix our signatures.

WILLIAM HOOPES. FRANCIS C. FRARY. JUN IUS D. EDWARDS.

v Certificate of Corretion. Y It is hereby certified that in Letters Patent No. 1,534,317, granted A' ril 21, 1925 u on the ap lication of William Hoopes, of Pittsburgh, and Francis unius D.

.Fi-ary dwards, of Oakmont, Pennsylvania, for an improvement in Electrolytic Production of Aluminum, an error appears in the printed specification requiring correction as follows: Page 10, line 33, claim 18, for the word from read upon; and that the said Letters Patent should be 'read with this correction therein that the same may conform to the record of the case in the Patent Oice.

Signed and sealed this'iSth day of August, A. D. 1925.

, [nml KARL FE'NNING, ,doti/ng Commissioner of Patents.

Certificate of Correction. l It is hereby certified that in Letters Patent No. 1,534,317, granted A' ril 21, 19253 :Jipon the aplication of William Hoopes, of Pittsburgh, and Francis Frary an unius D.

, dwards, of Oakmont, Pennsylvania., for an improvement in Electrolytic Production of Aluminum, an error appears in the printed specification requiring correction as follows: Page 10, line 33, claim 18, for the word from read upon; and that the seid Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this18th day of August, A D. 1925.

A [nm] KARL FENNING,

' Acting Commissioner of Patents.

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