US2785121A - Electrolytic apparatus - Google Patents

Description

March 12, 1957 A. H. JOHNSTON 2,785,121

ELECTROLYTIC APPARATUS Filed April 15, 1954 s Sheets-Sheet 1 IN V EN TOR.

Elan .6: .falmsfon/ BY RMvIW March 12, 1957 A. H. JOHNSTON ELECTROLYTIC APPARATUS Filed April 16, 1954 5 Shetg-Sheet a Mm s. MM,

March 12, 1957 A. H. JOHNSTON 2,785,121 I ELECTROLYTIC APPARATUS Filed April 15, 1954 s Sheets-Sheet 4 0 f'gte 72 4a 'IIIIII'IIIIIIIIIIIIIIII.

IN VEN TOR.

/Ila .falmsian/ aria/ENE) March 12, 1957 Filed April 16, 1954 A. H. JOHNSTON ELECTROLYTIC APPARATUS 'IIIIIIIIIA 5 Sheets-Sheet 5 INVENTOR.

Am/v H Jam 570w (imam l 2,785,121 1 Patented Mar. 1957 ELECTRGLYTIC APPARATU Alan H. Johnston, Arvida, Quebec, Canada, assignor to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada Application April 16, 1954, Serial No. 423,73a

11 Claims. (Cl. 294-247 This invention relates to apparatus for electrolysis of molten baths and more particularly to apparatus for electrolytic production of magnesium at the cathode of a fused bath, wherein a gaseous product such as chlorine is released at the anode.

A common method for so producing the metal involves passing an electric current through a bath that contains magnesium in halide form, the molten magnesium, which is lighter than the fused salts, being then collected as it rises from the cathode. The gaseous product of electrolysis, which is chlorine in the presently preferred type of operation using magnesium chloride, is collected separately above the anode, it being usually important to prevent contact between the liberated metal and the chlorine gas, since chlorine readily reacts with molten magnesium to form magnesium chloride. Indeed present experience is that the greatest over-all eificiency is to be expected in arrangements where there is a minimum of reconversion of magnesium to chloride form, if the cell is also at least reasonably economical in other respects and is satisfactorily convenient to operate and maintain.

A primary object of the present invention is therefore to aiford new and improved apparatus of the character and for the purposes described above, especially to enable the electrolytic production of magnesium in an eflicient, continuous manner and in relatively large quantities, While at the same time facilitating various necessary or incidental operations which contribute to economy and efiiciency in the process.

A presently preferred type of bath comprises magnesium chloride, usually in a somewhat minor proportion, together with other chlorides such as sodium and calcium chlorides and perhaps a very small amount of a fluoride, e. g. calcium fluoride, the materials other than the magnesium salt serving cooperative functions of increasing the fluidity of the bath, improving its conductivity and otherwise promoting the desired electrolytic action, all as will be readily understod. The bath i kept completely molten, conveniently by the heat of the electrolytic process. Not only is it important to keep the chlorine away from the liberated metal, but it is likewise desirable to prevent exposure of the cathode to chlorine at regions above the bath, since the chlorine will attack the cathode, which is usually made of iron or steel.

Various cell arrangements have been used or proposed to achieve these and other operating requirements, but in general such apparatus has been less than entirely satisfactory. For instance, because of structural difliculties, prior cells have often been of rather small or moderate size, so that a great number of units must he provided and separately attended in order to obtain a large output of the metal. This limitation of size has been especially serious Where the cell vessels have been lined with refractor materials rather than composed almost entirely of iron or steel, but in no such case has there been provision of effective, practical, large scale apparatus, for example wherein the magnesium metal might be collected at one place from many cathodes rather than at a plurality of places or in a multiplicity of separate cells. In some cell constructions provision has been made for progressive feeding of the graphite anode rods, and While such operation may be useful where the anodes are attacked because of moisture unavoidably introduced with magnesium chloride that has been produced by a wet process,'the stated cells are at the same time poorly adapted for collecting chlorine which is free of air or other contamination; yet it pure chlorine can be recovered, it can be employed for preparing anhydrous magnesium chloride by a dry process, and use of anhydrous salts in the electrolytic bath will avoid attack on the anodes.

For example, where magnesia is obtained in a dry state, as by' appropriate separation from ore in which magnesium compounds occur (e. g. the calcination of magnesite), an effective process for making essentially anhydrous magnesium chloride comprises treatment of the magnesia With chlorine gas in the presence of carbon, e. g. in a suitably heated furnace. If the chlorine derived from the electrolytic cell is to be economically employed for this high temperature method of producing magnesium chloride, it should be essentially pure, i. e. free of air or the like; hence the collection of uncontaminated chlorine is another desideratum of the cell itself.

Another problem which arises with magnesium cells, is the difliculty of sludge removal. During the operation of these electrolytic procedures, a considerable amount of sludge continuously accumulates at the bottom of the fused bath. Among other things, the sludge contains iron which is derived from the magnesium or other salts, and

lthough the iron does not seriously contaminate the molten magnesium that floats up, the accumulating sludge may not tend to clog the cell but will increasingly reduce the electrical efficiency, becauseits iron content provides a non-useful, low resistance path through a considerable region of the bath. Accordingly it is desirable to scrape or scoop the sludge from the bottom of the cell at frequent intervals, yet in a number of prior structures such work could only be accomplished by interrupting the electrical operation and removing some or all of the electrodes.

While in prior cells an effort has usually' been made with screening or shielding structures to separate the magnesium-collecting and chlorine-releasing regions at and above the bath surface, these arrangements, in cells of even moderately large capacity, have generally required delicate or ditficultly supported shapes of refractory material or the like. Such structures, however, are apt to need frequent repair or reconstruction, in that any chemical attack or deterioration by heat will seriously weaken or damage the special and relatively delicate refractory parts after a short time, especially Where the parts have to cooperate in the support of the anode or cathode.

Accordingly, a further object of the invention is to provide improved and efiicient apparatus for electrolysis of fused baths, wherein the various problems and difficulties described above are substantially overcome. A particular object is to afford a rugged, large capacity cell for the production of magnesium, the cell vessel being of refractory construction and having an unusually long life, against need for replacement or repair of refractory elements. Another special object is to provide an improved cell wherein molten magnesium may be collected, in a common region, from a multiplicity of separate cathodes, and wherein the evolved chlorine can be collected in a pure state, from a corresponding plurality of anodes and without attack on the cathodes or significant-reconversion of the liberated magnesium metal.

To these and other ends, including the provision of a novel cell adapted for ready practical achievement of the functions explained above, certain presently preferred embodiments of the invention are shown in the accompanying drawings and described below, by way of example to illustrate the features and principles of improvement.

Referring to the drawings:

Fig. 1 is a plan view of a multiple-electrode. cell embodying the invention, showing certain parts successively broken away and a portion in horizontal section;

Fig. 2 is a vertical section on line 22 of Fig. 1;

Fig. 3 is an enlarged vertical section of an anode mounting structure;

Fig. 4 is a vertical section on line 44 of Fig. 2;

Fig. 5 is a side elevation of a double cathode structure embodied in Figs. 1 and 4;

Fig. 6 is an end elevation of the cathode assembly of Fig. 5, from the left-hand end;

Fig. 7 is a horizontal View on line 7-7 of Fig. 5;

Fig. 8 .is a plan view of a part of a cell cover structure, such as shown in Figs. 1 and 4, with certain supplemental means;

Fig. 9 is a section on line 9-9 of Fig.8;

Fig. 10 is a vertical section on line 1010 of Fig. 2, on reduced scale; 7

Fig. 11 is a transverse vertical section similar to Fig. 2 and showing a modified structure; 7

Fig. 12 is a fragmentary view in vertical section, partly on line 12al2a and partly on line 1212-1212 of Fig. 11; and

Fig. 13 is a horizontal section of the cell of Fig. 11, on line 13-l3 of Fig. 12, on reduced scale.

Referring particularly to Figs. 1, 2, 4 and 10, the illustrated cell, which is especially designed for production of magnesium by electrolysis of a fused bath containing magnesium chloride, is enclosed in a box-like steel shell 20, externally reinforced and supported by appropriate structural steel work adjacent the walls as indicated at 21 and as provided by the supporting beams 22 beneath the bottom 24 of the shell. Inside the steel shell there is a horizontally elongated, rectangular main chamber generally designated 25 and a supplemental or metalcollecting chamber 27 extending parallel to the main chamber along one of the longer sides of the latter, specifically, the inner wall system of the cell, defining the stated chambers, is composed of refractory material, arranged in the nature of a lining of the steel shell but in fact essentially self-supporting like a massive structure of masonry. Thus the entire cell, constituting the two chambers and 27, has a rear wall 28, a front wall 29, end walls 30 and 31, a partition or curtain wall 32 separating the two chambers, and a floor 33.

The main chamber 25 is conveniently higher at the top than the other chamber, by reason of'upwardly extending refractory structures 34, 35, 36 and 37, respectively rising from the walls 28, 32, 3t and 31. The chamber 25 is closed by a refractory lined cover generally designated 40, which rests on the upper wall extensions just described and which has a detail construction as explained below. The supplemental chamber 27 may also, if desired, have a relatively light sheet metal cover 41 (aluminum or aluminum-faced) which may have a vent stack 42 and which can be arranged for ready removal to afiord access to the chamber 27.

The electrodes are disposed in the main chamber 25 and are conveniently large and generally rectangular members disposed in an upright position in a spaced parallel array, with the anodes and cathodes alternating. Thus the anodes may consist of heavy slab-like plates or blocks 44 of graphite, suspended from the cover 40, while the cathodes generally designated 45 are essentially steel or'iron plates, likewise of upright, rectangular, shape, arranged in an interleaved, spaced relation to the anodes. Specifically, in the cell shown, there are so-called single cathodes at the ends of the array (see Fig. 4), while between each successive pair of anodes there are two cathodes 45, constituting a double cathode assembly, for disposition efficiently close to the adjacent anodes while permitting appropriate spacing of the various electrode supporting and connecting instrumentalities in the cell wall or cover. As shown, the cathodes are wholly supported by metal plates 47 which extend through the rear wall 28 of the main chamber 25, so that all portions of the cathodes are kept below the fused bath surface approximately indicated by the dot-and-dash line 48 in Figs. 2 and 4. I

Trough assemblies generally designated 49 are mounted at the top edges of the cathode plates 45 and are arranged to slopeslightly upward from the end of the cathodes near the rear wall 28, toward and through the partition wall 32, the forward ends 5% of the troughs thus projecting into the supplemental chamber 27 through corresponding doors 52 in the curtain wall 32, such doorways being particularly shown in Fig. 10 (which for clarity shows only one cathode assembly) and also in dot-and-dash line in Fig. 4. Although in some cases other types of openings may be employed, or in some special instances a partition arrangement can be used which is in effect no more than an upper curtain that separate the two chambers at localities above the electrolyte level 48 (and a small distance beneath) and leaves the side of chamber 25 essentially entirely open below, the illustrated partition wall, with doorways as shown, represents a specific and important feature of improvement, afiording the desired results and at the same time embodying a relatively simple, rugged construction of self-supporting nature. It will be understood that in any event the two chambers communicate beneath the fused clectrolye, e. g. through the doorways 52, the molten salt level thus rising in the chamber 27 to such point as indicated at 54 in Fig. 2.

As will now be understood, metallic magnesium released by electrolytic action at the cathodes 45 rises along the sides of the latter, collecting under the trough assemblies 49 so as to travel along their sloping undersides to the chamber 27. There the molten metal rises from the ends 54 of the troughs, to collect as a supernatant layer 55 (Fig. 2) above the surface 54 of the molten salt. The other principal product of electrolytic action, viz. chlorine gas released at the anodes 44, rises above the electrolyte level 3 in the chamber 25 and may discharge through an appropriate pipe 57 at an upper part of one of the chamber walls (e. g. the upper wall extension 36 as seen in Figs. 1 and 4), the pipe 57 leading to a suitable locality (not shown) for use or other disposition of the essentially uncontaminated chlorine.

The described cell arrangement thus provides a relatively large, single, main chamber 25 wherein a plurality of anodes and cathodes of considerable size are supported in parallel alternating arrangement, for large production of magnesium. At the same time the troughs 4? and the partition wall 32 with its doorways 532 afford collection of the produced metal'in a single locality, viz. at the surface of the molten bath in the supplemental chamber 27, the metal being easily skimmed from the surface layer 55 at desired times (or drawn from a collecting well, not shown, at one end of the chamber). The partition wall 32 likewise completes the enclosure of the chlorine-collecting compartment, for the described separate removalyof pure chlorine.

.Referring now also to Figs. 5, 6 and 7, one form of a suitable structure for each of the double cathode assemblies comprises a pair of metal plates 45, e. g. of iron or mild steel, which may be of any desired dimensions (in one practical example, each was 2 /2 feet by 3 feet) and which are reinforced on their adjacent faces by smaller, overlappin plates 6% arranged in stepped relation, the reinforced plate structures being held and spaced apart by studs 61 and being secured along one vertical edge to a long, upright mounting block 62. The block 62 is carried at the end of the supporting plate 47, and if 'desired may be formed integrally therewith. As shown,

the block 62 is disposed between the cathode plate assemblies at the end locality of each where all of the reinforcing plates are secured to it, so that the entire double cathode structure is securely and rigidly held on the block and thus at the end of the mounting plate 47.

The plates 47 (Figs. 1 and 2) traverse the rear refractory wall 28 of the main chamber, through rectangular steel sleeves 63 that project from the housing 24, the plates being sealed in the sleeves by suitable means such as a thick layer of refractory cement 64, which also serves an electrical insulating function. Bus connections generally designated 65 are shown at the outer ends of the cathode support plates 47, and may extend, in a conventional manner, to the negative side of an appropriate source of direct current, not shown.

The trough assemblies 49 are heavy sheet metal structures comprising an inverted trough extending along and above the top of each cathode plate 45, and having downwardly and outwardly flaring skirts 67 which project over the outer sides of the plates, and similar, somewhat deeper skirts 68 above the inner surfaces. At the end adjacent the supporting plate 47, the long troughs 4 are joined by a like, transverse trough 69, similarly skirted and communicating with both of the others so as to form a long U-shaped trough structure which is thus adapted to collect any molten metallic magnesium rising from all faces of the cathode devices 45, 69, and both faces of the supporting block 62. The trough assembly is supported on the cathode plates by suitable brackets fastened at the upper edge of the latter.

At its opposite end from the support block 62, each trough 49 narrows, by virtue of funnel sections 71, to an inverted U-shaped section 72 which terminates in the upwardly flaring mouth 50. As shown in Figs. 1 and 2, the sections 72 project through the doors 52 of the partition wall 32 so that the molten metal leaving the trough months 50 rises to the surface 55 in the supplemental chamber 27. As also noted, the troughs, with their extensions 72, have a gradual upward slope from the transverse section 69 to the months 50, to promote the desired flow of the metal. While a small amount of magnesium may be electrolytically released at the upper surfaces of the iron or steel trough assemblies, and thus lost (in a temporary sense) by reconversion to magnesium chloride upon rising to the atmosphere of chlorine above the bath in the main chamber 25, the amount of metal involved and the current consumed in releasing it are found to be minor and thus to represent unimportant impairment of the over-all cell efiiciency, which is exceptionally high. If desired, these upper surfaces of the troughs may be faced with electrically insulating materials or alternatively the troughs may themselves be constructed of non-conducting refractory materials suitably attached to the cathodes. For effective avoidance of attack or corrosion, the cathode assemblies and troughs, all as supported by the plates 47 through a wall rather than the top of the cell, are entirely submerged in the bath at all times.

It will be understood that the cathode plates 45 are preferably so mounted as to afford the optimum value of anode to cathode distance for the actual dimensions, proportions and capacity of the particular cell or type of cell which is to be constructed in a given case. Such optimum value of electrode spacing (and consequently the value of voltage to be applied to the cell) should ordinarily be selected to yield the most efficient utilization of electrical energy in the apparatus; one advantage of the present invention is that the determination of such spacing can be readily facilitated, if necessary, by simple tests with adjustably mounted cathodes or adjustable cathode extensions, in a suitable prototype cell made as herein described and having the chosen size and other characteristics. Indeed it will be further understood that other arrangements or surface shapes of the cathode plates can be used, the chief requirement being to have lid an upright cathode assembly of generally extended shape disposed beneath the skirt 67 of the trough and providing relatively large, more or less upright surface structure closely facing the nearest anode slab.

The single cathode assemblies at the ends of the cell (Figs. 1 and 4), which each face an anode 44 only at one side, consist of a single, reinforced cathode plate 45, having a single trough assembly 49 with a like projecting portion 72 and a mouth 5!) opening in the supplemental chamber. The supporting assembly for each single cathode likewise (as shown) resembles the structure of block 62 and plate 47 for the double assemblies, but with the block projecting from only one side of the support plate toward the single cathode 45. As will also now be apparent,-the described mounting of both double and single cathodes through the wall 28 wholly supports all of them in spaced relation above the refractory floor 33, keeping them clear of any accumulating sludge and indeed facilitating the removal of the sludge itself. Where necessary or desirable for reasons of added mechanical strength or rigidity it is of course possible to provide additional support for the cathodes in the form of small refractory blocks or piers extending from the bottom of the cell to the bottom of the cathode at locations where such supports will not interfere with removal of the sludge.

The anodes 44 are shown carried by the cover assembly 40, from which they project downwardly into the bath. Although in some cases the anodes can instead be mounted to enter the cell sidewise through the rear wall 28 (between the cathodes) with equivalent electrolytic function and some of the other advantages (including separate removal of chlorine and magnesium), the top-entering anode mounting is particularly convenient, not only by reason of the removable nature of the cover assembly as described below, but also for avoidance of undue heating efiects, electrical leakage, and consequent deterioration as may sometimes occur (unless there is special cooling and insulation) in a wall through which both anodes and cathodes pass in close spacing.

The top assembly 40 comprises a metal, e. g. steel, shell having a frame of four upright side walls 78 and a transverse sheet 79 horizontally spanning the interior of the rectangular frame, so that the shell constitutes an inverted tray or pan, which is filled at its underside with a thick body of refractory material 80. The anodes 44 project through rectangular slots 81 in the refractory body and the cover plate 79. An upright rectangular sleeve 82 is disposed above each slot 81 to receive and support the corresponding anode 44, and is carried by a horizontal flange 83 at its lower end, appropriately bolted to the plate 79 (Pig. 3). A coil of pipe 85 surrounds each sleeve 82, for circulation of water or other coolant fluid to remove heat from the end portion of the anode and thus prolong the life of the assembled structure.

At their upper ends, the anodes 44 are secured between clamped assemblies 86, 87, which secure the lower ends of the bus bars 88 that extend to the positive side of the current supply (not shown), Although the anodes are shown as single slabs of graphite (or other carbon or simiiarly appropriate composition), it will be understood that each can be composed of a row of edgewise abutting vertical bars, the clamping means 86, 87 then serving to hold the bars in assembled relation so as to have the configuration of a single slab.

The actual support of each anode 44 is effected by the sleeve or bracket structure 82, in which the anode is suspended in sealed relation by appropriate means, such as a layer of magnesium 29 poured in place. The sleeves 82 are appropriately insulated (electrically) from the cover plate 79 by suitable gaskets 91 and by washer assemblies 2 surrounding the shanks of the bolt 93 by which the flanges 83 are secured to the plate 79. An open top box 95 is also carried at the upper end of each element 82, with its bottom wall closely fitting the anode.

After assembly, box 95 is filled with pitch or similarly suitable material (not shown) for effective seal of the upper ends of the anodes, i. e. so that the latter and the clamping parts 86, 37 are submerged in the sealing compound. As in the case of the cathodes additional mechanical support, though ordinarily unnecessary, may be provided in the form of small piers or blocks, supporting the anodes on the cell floor at one or more points.

A convenient feature of the described apparatus is that in first setting it up, and likewise at times when replacement of the anodes or other servicing may be required, the cover 40 can be assembled upside down, separately from the cell. To that end, the frame 7879 is appropriately supported in an inverted position with its normally lower cavity facing upward. The refractory material 89 is installed, and the sleeve brackets 82. having already been secured in place, in registration with the openings 81, the anodes are inserted and the magnesium metal 90 poured to hold them in sealed relation, the bottom of the box 95 in each case serving to retain the poured metal. The cover, thus holding the several anodes, is then hoisted and turned over and lowered into place at the top of the cell. The sides 73 of the cover shell depend skirt-like below the refractory body '84), so as to seat in a corresponding groove 97 which runs all around the upper edge of the refractory walls of the main cell chamber 25, i. e. in the top surface of the extensions 34, 35, 35 and 37 (Figs. 2 and 4). The groove 97, which is somewhat wider than the thickness of the cover sides 78 (that are now resting on the bottom of the groove), is then filled with pitch, chlorine-resistant cement, or other sealing material, so that the entire cover assembly is effectively yet removably sealed in place. Finally, the clamps 86, 87 and bus bars 88 are attached and the boxes 95 filled with pitch or the like as explained above. 7 While the entire filling 8b of the cover can be simply a body of plastic refractory, e. g. a cement poured and set in place (preferably with a slight clearance at the openings 81, around the anodes), some provision may be employed for keying the material, e. g. as detailed in Figs. 8 and 9. Thus the lower face of the transverse plate 79 may carry, at suitably distributed localities, pairs of downwardly depending, flanged metal brackets $9, each arranged to engage and retain the correspondingly grooved side walls of specially shaped refractory keying blocks 1%, which have downwardly and outwardly flaring sides and which thus facilitate the retention of the refractory cement 80 between them. A layer of insulation 102 may also be disposed between a major part of the refractory parts 80, 1%, and the cover plate 79, similar to the layer of like insulation 103 which immediately abuts the inner face of the cell casing 20.

While for simplicity in Figs. 1, 2 and 4, all of the main walls and floor of the cell are shown as if made of poured refractory material, it will be understood that these parts are conveniently and indeed preferably built of refractory brick, block or the like, as seen in Fig. 10, for superior structural strength and durability. Thus all of the outer, vertical walls of the cell, as likewise the floor, are built of refractory brick work, and also the parts of the partition wall 32 between the doorways 52, e. g. as indicated at 104 in Fig. 10. The upper part of the partition wall is similarly. made of brick or block structure, in the general manner of such masonry; for instance, the openings 52 are spanned by suitably keyed or tapered blocks 165, the remainder of this course being completed with other blocks tee of opposite taper. Finally, the uppermost wall portion 35 may comprise several courses of shnple, refractory brick work. Thus the entire refractory structure of the cell is ruggedly built of bricks or blocks, in an essentially self-supporting manner, and is such as to be capable of continuous use for very long periods of time without need for repair or reconstruction.

As stated, normal operation of the cell with a fused halide bath containing magnesium chloride tends to produce a certain amount of sludge which settles to the bottom, particularly in the main chamber 25. By virtue of the supplemental chamber 27 (easily accessible upon removal of its cover 41), suitable long-handled rakes or scrapers can be inserted downwardly into the body of molten salt and through one or another of the doors 52, and can then be used to rake the accumulated sludge along the bottom 33 from the vicinity of the rear wall 23 to and through the doors. Thus brought into the supplemental chamber 27, the sludge may be scooped up and out of the bath with the same or other longhanded instruments.

it will be noted that the spacing and disposition of the double and single cathodes is such as to facilitate sludge removal, the spacing studs 61 of the double cathodes being located only at localities above a diagonal line across the plates 45 (Pig. 5), to allow the handle of the collecting instrument to pass between the plates. If desired, raised sections or curbs 108, having downwardly sloping faces 1% along their upper sides, may be built up from the floor beneath the anodes 44 at localities between the doorways 52. These curbs, above which the anodes hang in spaced relation, serve to channel the sludge into the localities beneath the cathodes, for most effective removal as described above. It will now be seen that in the present cell, sludge (which may impair the electrical efficiency by reason of its iron content) can be easily cleared out as often as desired, e. g. every few days or oftener.

The described cell is adapted for operation with molten salt baths of various compositions, one satisfactory example being as described qualitatively hereinabove and containing, for instance, about 15% magnesium chloride, 30% calcium chloride, sodium chloride and a small amount of calcium fluoride, i. e. 5% or less. The operating temperature in the 700 C. or so; for example, excellent results have been obtained when it is maintained at 720 plus or minus 30", the entire heat (during continuous operation) being obtained from the electrolytic action itself.

From time to time a so-called bleeding operation may be required with a bath of the above type, when the calcium chloride content becomes too high by reason of additions of such salt as an impurity in the magnesium chloride. To perform such operation a siphon tube is simply inserted in the supplemental chamber 27 to siphon off a suitable amount of the molten electrolyte, which is then replaced with an appropriate mixture containing only the other bath ingredients. For instance, the calcium chloride can thus be kept between 25% and 40%, to provide an average content of about 30%. it will be understood that as the magnesium chloride itself is depleted by the desired electrolytic action producing magnesium and chlorine, further quantities of this salt are added through the chamber 27, if desired in molten form. The operation of the cell has been essentially explained throughout the foregoing description. At the outset, assuming that the apparatus is fully assembled, with the cover and anodes in place, the cell is filled with the salt mixture, conveniently in molten form, and suitable current supply is then initiated to the bus bar 65, 38. Electrolytic action proceeds efiiciently, causing accumulation of essentially pure chlorine gas in the upper part of the main chamber 25, from which it may be continuously withdrawn through the pipe 57, as for effective use in the dry process of making magnesium chloride. At the same time, metallic magnesium of hi h purity, is continuously collected under the troughs 49 and delivered to the supplemental chamber 27, where it may be removed as described above. The entire operation may run continuously for an indefinite period of time,'usual1y requiring only regular replacement of magnesium chloride and other supplemental steps as explained.

As will be appreciated, any of various refractory materials can be used for the walls, floor and roof of the cell,

cell is usually of the order of V such as good: quality fire clay brick, or other aluminum lihood of attack, e. g. in the vicinity of the electrolyte surfaceor at regions of contact with molten magnesiumv Not only are the described results of efiiciency and convenience achieved by the cell, but it may have an unusually large capacity, i. e. by employing a multiplicity of anodes and cathodes (as shown) and without requiring the individual electrode elements to be unduly cumbersome or diiilcult to support. Indeed the specific number of electrodes shown is merely illustrative; for example, with the cell chambers longer, still greater numbers of anodes and cathodes may be employed if desired. The supplemental chamber 27 is preferably relatively narrow, i. e. as shown "in Fig. 2; it should be small enough to keep its portion of the bath molten (by conduction of heat from the main chamber 25), but large enough to alford convenient removal of magnesium metal and ready access to'the main chamber, through the doors, for de-sludging. The

electrolytic action is advantageously restricted, in effect,

' to the main chamber 25 which is fully sealed at all localities above the bath surface, to prevent undesirable leakage of chlorine. As also explained, the removable cover structure 48 has various specific advantages and so supports the anodes that they, like the cathodes, are wholly elevated from'the bottom of the cell, it being difiicult to hold large anodes in other ways without resting them on the cell floor or suitable pedestals.

In Figs. ll, 12 and 13 a modified structure of inverted troughs over the cathodes is illustrated, it being understood that these views represent a simplified illustration of the cell in other particulars in that many details have been omitted for clarification but may be identical, in use, with what is shown in the preceding figures. The cell in Figs. ll, 12 and 13 embodies the same walls 28, 29, 30, 31 and 32, which together with the floor 33 define the main chamber 25 and the supplemental chamber 27. Thesame array of anodes 44 are provided, suspended from the cover 40, with cathodes between successive anodes, carried by the members 47 through the rear wall 28. For variety of illustration, the cathodes 45a are shown arranged to slope outwardly at the bottom, i. e. toward the adjacent anodes, with some advantage in efficiency by reason of a shorter average electrical path between cathode and anode.

The troughs over the cathodes, for conducting molten metal through the doorways 52 into the supplemental chamber 27, are made of refractory material, and specifically consist of single, monolithic blocks 120, 121 which at their ends are embedded in and supported by the rear refractory wall 28, and at their forward ends are disposed within, and as part of, the curtain wall 32, each block being conveniently sufliciently wide so that the side portions of its bottom rest, at this locality, on upper faces or shoulders of the refractory brick work 104 constituting the upright supporting portions of the wall 32 between the doorways 52.

As shown, the underside of each of the blocks 120, 121 is hollowed out at 122, 123 respectively to provide an inverted trough-like contour above the cathodes, the underside of each block and the surface of the inverted troughs 1 22, 123 being arranged to slope slightly upward fromthe vicinity of the rear wall 28 to the forward ends 'of the blocks, in the side of the w all 32 facing the V chamber 27. As will be seen, the blocks 120 which are By the provision of the inverted trough structure in the form of these refractory blocks 12%, 121, some improve- 'ment of electrical efficiency is obtained, e. g. in that there is no current lost in releasing magnesium metal at the upper surface' of metal trough structures where such recombine with chlorine.

magnesium cannot be collected and thus simply rises to At the same time the cathodes 45a and their supports 47 are relieved of mechanical load of the troughs, the blocks 12%, 21 being very elfec-tively supported by the heavy refractory walls 32, 28. Since the distance across the cell spanned by these blocks is relatively short (an advantage of the cell being that its large capacity is obtained by the arrangement of successive anodes and cathodes arrayed through the considerably greater length of the chamber 25 in the other direction), the blocks can be supported at their ends as shown and yet can be inherently of suflicient strength so as not to crack orbreak over extended periods of service.

These blocks, of course, may be constructed of conventional refractory material named above, made in the usual fashion of casting or molding pro-formed bodies of such material. While in the cell of Figs. 11 to 13 inclusive the blocks are shown as particularly massive for optimum strength and thus such that the bath level 48 within the chamber 25, and likewise the levels 54, 55 in the chamber 27 are intermediate the top and bottom of each block, it is contemplated that shallower blocks may be employed in some cases such as to be wholly submerged in the bath, with the advantage that there is then less attack on the refactory material such as is particularly greatest at the electrolyte-to-atrnosphere interface. The function and effect of the inverted troughs over the cathodes constituted by the blocks 120, 121 is exactly as described above rela tive to the troughs 49 in Figs. l to 10, namely in collecting the molten magnesium which rises from the cathodes and in conducting such metal to the supplemental chamber 27, where it further rises to the surface for removal.

T his application is a continuation-in-part of my copending application Serial No. 274,377, filed March 1, 1952 for Electrolytic Apparatus, now abandoned.

it is to be understood that the invention is not limited to the specific apparatus herein shown and described, but i may be embodied in other forms without departure from 'rising and supported from the bottom of the cell and dividing the cell into main and collecting chambers, said partitioning wall having open regions therein spaced below the top of the cell for communication between the chambers, the aforesaid wall structure including a wall for the main chamber opposite the partitioning wall, cover means closing the main chamber, means for ex- 7 hausting gas from the main chamber above the fused bath, a plurality of cathodes in parallel array in the main chamber, each cathode being disposed crosswise of the main chamber between the partitioning wall and said opposite wall and each cathode having substantial extent both vertically and crosswise of the main chamber, means extending laterally through wall structure of the main chamber other than the partitioning wall and spaced below the top of the cell, for support of and electrical connection to said cathodes, anode means between said cathodes in mutually facing relation therewith, and means providing inverted trough surfaces over the cathodes, extending'across the main chamber and through the partitioning wall, for leading molten metal released at the cathodes into said supplemental chamber, said cathodes being disposed below the said trough surfaces, and said cell Wall structure having upper parts and said partitioning wall having an upper portion, said parts and portion being above, and being arranged to hold fused bath in both chambers to a level wholly above said inverted 2.'Appar'atus' as described in claim l,"wherein said main and collecting chambers have a refractory floor that extends across both, and wherein the partitioning wall includes supporting refractory portions extending upward from said floor, the open regions of the wall being constituted by doorways therein between said supporting portions, said doorways extending downward to the floor and providing access from the top of the collecting chamber through the fused bath to the floor of the main chamber for removal of sludge from said main chamber floor, said doorways extending upward to the localities of the inverted trough surfaces, and said inverted trough means being arranged to guide the molten metal into the collecting chamber through the doorways at upper portions of the latter.

3. Apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, comprising refractory wall structure defining a fused bathreceiving cell, a self-supporting partitioning wall of refractory material extending from the bottom of the cell and partitioning the cell into main and collecting chambers, the aforesaid wall structure including a wall for the main chamber opposite the partitioning wall, cover means closing the main chamber, a plurality of cathodes in parallel array in the main chamber, each cathode being disposed crosswise of the main chamber between the partitioning wall and said opposite wall and each cathode having substantial extent both vertically and crosswise of the main chamber, anode means between said cathodes in mutually facing relation therewith, said partitioning wall having open regions therein spaced below the top of the cell for communication between the chambers, said collecting chamber and said open regions being cooperatively shaped and arranged to provide mechanical access down through the collecting chamber and said open regions to and across the floor of the main chamber, and molten metal collecting means providing guiding surfaces extending across the main chamber over the cathodes and opening into the collecting chamber at calities higher than the cathodes for delivering molten metal from the cathodes into the collecting chamber, said cell wall structure having upper parts and said partitioning wall having an upper portion, said parts and portion being above, and being arranged to hold fused bath in both chambers to a level wholly above said guiding surfaces, cathodes, and open regions, said partitioning wall wholly separating the chambers at its said upper portion.

4. Apparatus as described in claim 3, wherein said main and collecting chambers have a refractory floor that extends across both and wherein the partitioning wall includes supporting refractory portions extending upward from said floor, the open regions of the wall being constituted by doorways therein between said supporting portions, said doorways extending downward to the floor and being disposed in registration with the adjacent ends of the aforesaid cathodes, said apparatus also including means disposed below said metal guiding'surfaces and extending laterally through the aforesaid opposite wall of the main chamber to the cathodes for support and electrical connection thereof.

5. Apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, comprising refractory wall structure and a refractory floor defining a cell vessel for receiving the fused bath, a selfsupporting refractory wall extending upward from the floor of the cell vessel and dividing said cell vessel into main and supplemental chambers, mutually spaced cath-' odes and anode means arranged in alternate parallel array in the main chamber and extending transversely thereof relative to the said dividing wall, each cathode having substantial extent both vertically and in a transverse direction relative to the dividing wall, means extending through wall structure of said main chamber spaced from said dividing wall for supporting said cathodes above the floor, cover means sealing the top of the main chamber and comprising refractory material facing said main chamber, means carried by said cover means for suspending said anode means, said dividing wall having doorways at the ends of the cathodes, extending down to the floor and providing access through the supplemental chamber and the fused bath to the floor across the main chamber, and inverted troughs over the cathodes extending through the doorways for leading the produced metal from all the cathodes into the supplemental chamber, said doorways having their upper ends above the cathodes, said refractory wall. structure having upper parts and said dividing wall having an upper portion, said parts and portion being above, and being arranged to hold fused bath in both chambers to a level wholly above said doorways and cathodes and above the paths of metal along the inverted troughs, said dividing wall wholly separating the chambers at its said upper portion.

6. Apparatus as described in claim 5, wherein the cover means comprises an inverted tray-like shell lined below with refractory material and disposed on said dividing wall and the portions of said refractory wall structure which complete the boundary of the main chamber, said anode means comprising a plurality'of upright anodes extending through the cover means and supportedwithin the main chamber and above the floor thereof by said suspending means, said suspending means holding said anodes in sealed relation to the cover means, said cathodes comprising at least several upright cathode structures interspersed with said'anodes to constitute said alternate array, each of said anodes and cathode structures being sustantially perpendicular to said dividing wall and said cathode supporting means comprising metallic supporting members traversing the wall of the main chamber opposite the supplemental chamber, for respectively holding the cathode structures.

7. Apparatus as described in claim 5, wherein the cover means comprises an inverted tray-like metal shell partially filled with refractory material throughout its under cavity and having depending metal skirt portions around its periphery, said dividing wall consisting of preformed refractory shapes laid up in self-supporting relation upon and from the floor of the cell, said dividing wall and the portions of said refractory wall structure which complete the boundary of the main chamber having grooves along their upper edges, the aforesaid metal skirt portions of the cover being seated and sealed in said grooves.

8. Apparatus as described in claim 5, wherein said inverted troughs comprise refractory blocks each having a trough-like contour on its underside and each supported at its ends respectively in a portion of the first-mentioned wall structure of the main chamber opposite the dividing wall, and in the said dividing wall at localities bridging the doorways.

9. Apparatus as described in claim 5, wherein the said self-supporting dividing wall consists of preformed refractory shapes laid up in self-supporting relation upon and from the floor of the cell vessel, said refractory shapes being mutually disposed to provide the aforesaid doorways and to constitute the aforesaid upward extent of thedividing wall.

10. Apparatus for electrolytic production of magnesium at the cathode of a fused bath releasing chlorine gas at the anode, comprising a vessel for receiving the fused bath, said vessel being internally faced with refractory material, a plurality of upright cathodes arranged in spaced, parallel array in said vessel, each cathode having substantial extent both vertically and crosswise of the array, supporting and connecting means for said cathodes extending through a side wall of said vessel, a plurality of vertical anodes arranged in spaced parallel array in the vessel, said anodes being interspersed between the cathodes in spaced relation thereto, said vessel having cover means enclosing it at the top, means extending through said cover means for support of and connection 13 to said anodes, said vessel including means for discharge of chlorine gas collected above the bath, said vessel having another side wall opposite the first-mentioned side wall and extending transversely of the cathodes, said second side wall consisting of refractory material rising and supported from the bottom of the vessel, said vessel including means internally faced with refractory material and providing a suplemental chamber along the outer side of said second side wall, said supplemental chamber extending upward from the aforesaid bottom of the vessel, said second side wall including a plurality of doorways spaced lengthwise thereof and disposed at a lower part thereof in registration with the adjacent ends of the cathodes, said second side wall preventing access between the supplemental chamber and the vessel above the doorways, and said doorways and said supplemental chamber being shaped to provide access from the top of the supplemental chamber through the fused bath to the bottom of the vessel for mechanical removal of sludge from said bottom, and molten magnesium-collecting means extending along upper portions of the cathodes and including means guiding molten magnesium into the supplemental chamber through the doorways, for delivering said magnesium from all of the cathodes into said chamber, said vessel, including its said second side wall and its said 25 supplemental chamber means having sufiicient upward extent to receive fused bath in the vessel and supplemental chamber to a level in each which is wholly above said doorways, cathodes, and cathode-supporting and connecting means, and above the paths of molten magnesium along the collecting means.

11. Apparatus as described in claim 10, wherein the magnesium-collecting means for the cathodes consist of a plurality of refractory blocks above the cathodes and arranged with the anodes interspersed between said blocks, each block having an inverted trough contour at its underside and being supported at its ends respectively in the first-mentioned side wall of the vessel and in the secondmentioned side wall in bridging relation to said doorways.

References Cited in the file of this patent UNITED STATES PATENTS 607,506 Danckwardt July 19, 1898 1,074,988 Steinbuch Oct. 7, 1913 2,401,821 Gardiner June 11, 1946 2,432,431 MacMullin Dec. 9, 1947 FOREIGN PATENTS 740,731 France Nov. 21, 1932

Claims (1)

1. APPARATUS FOR ELECTROLYSIS OF A FUSED BATH TO PRODUCE AT THE CATHODE A METAL LIGHTER THAN THE BATH, COMPRISING REFRACTORY WALL STRUCTURE DEFINING A FUSED BATHRECEIVING CELL, A PARTITIONING WALL OF REFRACTORY MATERIAL RISING AND SUPPORTED FROM THE BOTTOM OF THE CELL AND DIVIDING THE CELL INTO MAIN AND COLLECTING CHAMBERS, SAID PARTITIONING WALL HAVING OPEN REGIONS THEREIN SPACED BELOW THE TOP OF THE CELL FOR COMMUNICATION BETWEEN THE CHAMBERS, THE AFORESAID WALL STRUCTURE INCLUDING A WALL FOR THE MAIN CHAMBER OPPOSITE THE PARTITIONING WALL, COVER MEANS CLOSING THE MAIN CHAMBER, MEANS FOR EXHAUSTING GAS FROM THE MAIN CHAMBER ABOVE THE FUSED BATH, A PLURALITY OF CATHODES IN PARALLEL ARRAY IN THE MAIN CHAMBER, EACH CATHODE BEING DISPOSED CROSSWISE OF THE MAIN CHAMBER BETWEEN THE PARTITIONING WALL AND SAID OPPOSITE WALL AND EACH CATHODE HAVING SUBSTANTIAL EXTENT BOTH VERTICALLY AND CROSSWISE OF THE MAIN CHAMBER, MEANS EXTENDING LATERALLY THROUGH WALL STRUCTURE OF THE MAIN CHAMBER OTHER THAN THE PARTITIONING WALL AND SPACED BELOW THE TOP OF THE CELL, FOR SUPPORT OF AND ELECTRICAL CONNECTION TO SAID CATHODES, ANODE MEANS BETWEEN SAID CATHODES IN MUTUALLY FACING RELATION THEREWITH, AND MEANS PROVIDING INVERTED TROUGH SURFACES OVER THE CATHODES, EXTENDING ACROSS THE MAIN CHAMBER AND THROUGH THE PARTITIONING WALL, FOR LEADING MOLTEN METAL RELEASED AT THE CATHODES INTO SAID SUPPLEMENTAL CHAMBER, SAID CATHODES BEING DISPOSED BELOW THE SAID TROUGH SURFACES, AND SAID CELL WALL STRUCTURE HAVING UPPER PARTS AND SAID PARTITIONING WALL HAVING AN UPPER PORTION, SAID PARTS AND PORTION BEING ABOVE, AND BEING ARRANGED TO HOLD FUSED BATH IN BOTH CHAMBERS TO A LEVEL WHOLLY ABOVE SAID INVERTED TROUGH SURFACES, CATHODES, CATHODE SUPPORT MEANS, AND OPEN REGIONS, SAID PARTITIONING WALL WHOLLY SEPARATING THE CHAMBERS AT ITS SAID UPPE PORTION.

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