US2957816A

US2957816A - Apparatus for fusion electrolysis of reactive metals

Info

Publication number: US2957816A
Application number: US716322A
Authority: US
Inventors: Ralph M Sarla; Ernst O Schneidersmann
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1958-02-20
Filing date: 1958-02-20
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25

Description

Oct. 25, 1960 R. M. SARLA ET AL APPARATUS FOR FUSION ELECTROLYSIS OF REACTIVE METALS Filed Feb. 20, 1958 2 Sheets-Sheet 1 Depsi1ed` Material "aan IN VEN TORS RALPH M. SARLA ERNST O. SCHNEIDERSMANN TTOR EV Oct. 2K5, y1960 R. M. sARLA ETAL 2,957,816

APPARATUS P0P FUSION ELECTROLYSIS oF REACTIVE METALS Filed Feb. 20, 1958 2 Sheets-Sheet 2 INVENToRs A' RALPH M. sARLA alg ERNST o. scHNElDERsMANN 19V/MAJ- le 07%,.

ATTORNV APPARATUS FOR FUSIN ELECTROLYSIS OF REACTIVE METALS Ralph M. Sarla, Ramsey, NJ., and Ernst O. Schneidersmann, Wanne-Eickel, Germany, assignors to Union Carbide Corporation, a corporation ofNew York Filed Feb. 20, 1958, Ser. No. 716,322

v 6 Claims. (Cl. 204--225) ThisV invention relates to a high-temperature cell for the-fusion electrolysis of the high meltin-g point reactive metals of groups IV, V and VI of the periodic table. More specifically, the invention is concerned with a cell for the electrolysis of the halides of such reactive metals in a fused salt bath consisting of alkali or alkaline earth metal halides.

\ Reactive metals of groups IV, V and VI of the periodic table are prone vto embrittlement if contacted withair at the hightemperatures at which their fusion electrolysis production is conducted. The inherent susceptibility of these metals to contamination by oxygen and nitrogen, particularly,` requires `that certain measures be taken to protect these metals .when they are still in their pure, newly deposited,` form.

The most successful measure instituted to maintain the purity of the deposited reactive metal is to perform the electrolysis `under vacuum or under the protective shield of an inert gas. Although this method of present-day practice is entirely successful, removal of the cathode ony which the metal is depositedin the fused salt bath is eventually necessary, entailing interruption of the entreprocess'. The reactive metal deposit, once withdrawn, must then' be allowed to cool, since its exposure to the atmosphere in its hot condition would quickly negate the purity protection afforded it Within the shielding enclosure of the cell. This cooling period, however, is sufficiently long to allow solidiiication of the salt bath, which must then be remelted for the next operation. A batch-type operation of this nature increases the cost of the metal considerably and represents an extremely ineflicient method of production, for the cell is idle almost as long as it is productive.

The high temperatures necessary in Ithe fusion electrolysis of the refractory metal halides, and the readiness of the pure metals to react in the atmosphere have, until now, prevented the development of a continuous or semicontinuous method for removal of the cathode products. 7 With a View to overcoming such prior art shortcomings, it is an object of this invention to provide an electrolytic cell which is compatible with a practically continuous production of high melting point reactive metals by fusion electrolysis.

A further object of the invention is -to provide an electrolytic cell which operates under conditions which exclude air or moisture Iat elevated temperatures, is simple to control, and is capable of continuously producing reactive metals of high purity.

, These and other objects and advantages are achieved by the incorporation in an electrolytic cell of -an assembly having a plurality of cathodes which can be shifted from side to side over the cell entrance while maintaining an eifective gas tight seal.

l Referring now to the attached drawings,

Fig. 1 illustrates, in cross section, the lapparatus of the invention.

Fig. 2 is an enlarged sectional side view of the appa- '2,957,816 Patented Oct. 25, 1960 ratus shown in Fig. 1 and indicates other features of the subject electrolytic cell.

Figs. 3 and 4 are side elevational Views of the carriage? bearing assembly for raising the upper cell portion.

Referring now to the drawings, to show clearly the position of O-ring seals which make possible the con-V tinuous exchange cathodes, the lower cell assembly, cornprising the cell, is shown from the top in Fig. l and the upper assembly, which permits cathode exchange, is shown from the bottom. This assembly consists of a water-cooled gas-tight chamber 1 containing a graphite crucible 2 which serves as the anode. A plate 3 of conducting material may be pressed against the bottom of the Crucible 2 to make electrical contact.

surrounding the entrance to the chamber and extending outward, a table member 6 with a smoothly-nished sur- 6. An oval O-ring 10 composed of synthetic plastic,`

such as polyethylene, resistant to cell eluents, encircles the two openings of the

cathode chambers

8a and 8b and is depressed by the weight of the upper assembly so as to seal the combined cathode and cell chambers effectively from the atmosphere. n

Assuming the position of the apparatus as indicated in Fig. l, the lower opening o-f cathodechamber 8a is in' vertical alignment with the cell opening, around which a secondary O-ring 11 is secured. This additional seal supplements O-ring 10 in actual operation but has an a even more important function in maintaining an independent seal between

cathode chambers

8a and 8b when one is opened to the atmosphere for removal of the metal from the deposition cathode tip.

The cathode 12a in central alignment Wit-h the Walls of the chamber 8a can be lowered through the opening in the lid 13 Aand is assisted in remaining truly vertical by a seal 14 as the cathode tip is submerged in the electrolyte in the Crucible 2, thus completing the electrical circuit.

Unexpectedly, it w-as observed that a conical tip cathode was not attacked by gas evolved from the anodic bottom of the cell. For best results it was found that the distance o-f the tip of the cathode from the bottom of the anodic Crucible should be greater than the space betweenthe cathode andthe crucible wall. When these clearances `are maintained, preferential growth of the deposit on the tip of the cathode and subsequent shorting out ofthe D.C. circuit `between the cathode and the Crucible bottom are prevented. The cathode construction is preferably of cold rolled A nickel and that portionof the shaft immediately above the conical tip may be protected from cell gas by `a simple carbon or graphite sleeve. The cathodes are further preferably protected by air-cooling means as indicated by the `arrows at the top of cathode 12a in Fig. 1. Y

Picturedin Figs. 3 and 4 are the quick-acting clamps and carriage-bearing assembly for raising the upper cell portion. The toggle clamp 15, when depressed, lowers the shaft 16 so that the Wheel 17 presseson the table 6 and raises the carriage 9. When the section is thus lifted, the holding lug 17a is also released and the entire assembly may be easily shifted, so that chamber 8b lies in vertical alignment with the cell opening. Clearance between carriage 9 and table 6 is so adjusted that O-rings 11 and 12 are partially compressed even while carriage 9 is in the raised position. -A gas-tight seal may thus be The crucible.' 2 is surrounded by -a heating system 4 and is insulated, f from the chamber 1 by refractory material 5. Completely v maintained at all times. Release of the clamps compresses the oval O-ring seals 10and 11, and immediate lowering of cathode 12b allows continuation of the reactive metal deposition.v This procedure permits practically continuous electrolysis, since the'deposited material on the tip of the cathode 12a now has ample time to cool, and is subsequently removed,v through the'lid 13. The cathode chamber 8a is evacuated and. is then ready for reuse as soon as the cathode 12b, which isat that time being employed, requires removal of deposited metal.

As will be noted in both Figs. l and 2, the Olrings 10 and =11 are situated in a manner that will preventV conflict withv each other when the exchange of cathode chambers is effected. During this movement, when neither

chambers

8a or 8b are resting on O-ring 11, both'chambers are in evacuated or inert gas-filled condition'. An alter'- nate method for providing a workable, positive seal means is to place a sheet of polyethylene or other suitable plastic between the sliding carriage and the table. Such material acts as an infinite number of O-rings and allows the cathode chambers to be Sealed in any position.

Another effective method for maintaining a gas-tight seal without the use of an oval-ring is possible. This may be done by providing multiple rings similar to O-ring 11l along the surface of table 6. These rings should be spaced at intervals equal to the distance between cham bers 8a and y8b so that the bottom opening of each suchl chamber will be encircled by such a ringy during operation. Any number of rings may be so provided to correspond with any desired number of cathode chambers.

The entire procedure for shifting cathodes takes but a moment and is extremely simple, inexpensive, compatible with maintaining the purity of the metal depositedl on the cathode and makes possible a practically continuous operation. The salt bath, or electrolyte, is under constant protection from air and moisture, and the temperature within the cell is always sufficiently high to prevent its solidification, especially during cathode changes.

In preparing for actual operation of the apparatus of the invention, a fused electrolytic salt mixture is fed into the cell. Suitable electrolytes containing alkali metal halides and alkaline earth metal halides, and a chloride of the desired reactive metal are disclosed and claimed in the copending application of R. M. Sarla, Serial No. S 12,297, filed May 3l, 1955. The upper'and lower assemblies are aligned in secure position with the 0rings depressed to exclude the atmosphere. The cathode of the chamber in use is held in readiness to be lowered into the electrolyte. Referring now to Fig. 2, the cell is evacuated through an outlet 1-8 to approximately 100 microns after which the chamber and cell may be flooded with an inert gas, such as argon, through the inlet 19. or the operation may proceed under pressures below atmospheric. The temperature within the cell is now elevated to melt the salt and when fusion is complete, the refractory metal halide, which may be gas, liquid or solid, is fed in and combined with the fused salt bath through the opening to form the electrolyte. All is now in readiness for submergence of the cathode into the electrolyte for completion of the electrolysis vcircuit and for deposition vof the pure reactive metal on the cathode tip. The halogen gas which is evolved at the anode rises to fill the area above the electrolyte and is either eliminated by suction through `the outlet 21 or by cycling the inert gas.

To offset the possibility of corrosive action by the halogen gas at the elevated temperature within the cell, a series of inlets, hollows, and outlets honeycomb the apparatus for circulation of water for cooling various'portions of the equipment independently of each other. Fig. 2 illustrates the sectionsof the apparatus'which are so cooled, and these include, progressing fromthe lower portion to the upper, the anode, shell, under-portion of the table, cathode chamber, cathode chamber lid andthe cathode itself. By so cooling the entire assembly, not only is the corrosive action of the evolved gas negated, but the seals are protected from burning, or even losing. their resiliency.

It is to be understood thata number of modifications may be made in the apparatus of the invention without departing from the spirit thereof. For example, the anode and cathode chambers may be of any desired configuration which would assist in the electrolysis and collection of the end metallicproduct. While the anode chamber as shown is externally heated, it would also be quite` feasible to heat said chamberinternally, as by heating elements inserted in the crucible.

Subject matter particularly related'to the'electroly'tic mixtures suitable for use in conjunction with the previously described cell is disclosed and claimed in my copending application Serial No. 512,297, filed May 31. 1955.

'Ihis application is a continuation-impart of application Serial No. 631,185, filed December 28,' 1956, now aban-A doned, by R. M. Sarla, entitled ApparatusforProducing Tantalum, and application Serial No. 631,186, filed" December 28, 1956, now abandoned, by R. M. S'arla" and E. O. Schneidersmann, entitled Apparatus for'Fus'on Electrolysis of Reactive Metals.

What is claimed is:

l. In an electrolytic cell for the production ofhigh melting point reactive metals of groups IV, V and VI of(y the periodic table by the deposition thereof` from an" electrolytic bath, the combination comprising a lower cell assembly consisting of a water-cooled chamber containing a crucible serving as the cell anode, heatingm'eans for heating the contentsv of said Crucible,l a table member surrounding the opening to saidchamb'er at the upper" removably mounted therein; sealing means between said' assemblies; means for supplying electric currentto'said' anode and cathode; feeding means for introducing an electrolytic charge into said cell; and means for evacuating and for injecting inert gas in said cell andV cath'o'd'e' chamber.

2. The cell of claim 1 whereinrefractory material is' provided between said vacuum chamber and crucible for' insulation. Y

3. The cell of claim l wherein plastic O-rin'gs' encircle the openings of the cathode chambers, and of the vacuum' chamber to provide an effective seal again'st'the atmos` phere.

4. The cell of claim l wherein plastic O-rings encircle` the opening of the anode chamber and are intervallicly spaced along said table member to seal each oflsaid cathode chambers.

5. The cell of claim 2 wherein the distance from`th'e tip ofV said cathode tothe bottom of saidcmcible is` greater than the distance from said cathode to the wall of said Crucible.

6. In an electrolytic cell for the production vof high melting point reactive metals of groups IV, V and VI of the periodic table, said cell having an inlet for receiving a cathode therein, a cell cover assembly to provide for substantially continuous production of metal whichv comprises a table member fitted to the top of said'ell and having an opening to permit .the passage of a cath` ode therethrough into said cell, a base member movably mounted upon said table member, a plurality `of chambers adapted to contain cathodes fixedly' and sealably mounted on said base member,v said' chambers" having lower outlets therein extending through said base member .to permit asaid cathode to be lowered into said cell upon moving said kbase member on said tablejmember t9 align a said chamber with said cell, annular' sealv 5 6 ing means fixed to the lower surface of said base memcontinuously sealing said chambers and said cell from ber to surround said chamber outlets and to compressibly the atmosphere. and continuously contact the upper surface of said table v References Cited in the me of this patent member, said base member and affixed sealing means arranged upon said table member to be movable thereon 6 UNITED STATES PATENTS to permit alternate alignment of said chambers with said 1,838,666 Fink et al. Dec. 29, 1931 cell and alternate employment of cathodes therein while 2,760,930 Alpert et al. Aug. 28, 1956

Claims

1. IN AN ELECTROLYTIC CELL FOR THE PRODUCTION OF HIGH MELTING POINT REACTIVE METALS OF GROUPS IV, V AND VI OF THE PERIODIC TABLE BY THE DEPOSITION THEREOF FROM AN ELECTROLYTIC BATH, THE COMBINATION COMPRISING A LOWER CELL ASSEMBLY CONSISTING OF A WATER-COOLED CHAMBER CONTAINING A CRUCIBLE SERVING AS THE CELL ANODE, HEATING MEANS FOR HEATING THE CONTENTS OF SAID CRUCIBLE, A TABLE MEMBER SURROUNDING THE OPENING TO SAID CHAMBER AT THE UPPER PORTION THEREOF, AND EXTENDING OUTWARDLY THEREFROM, AN UPPER CELL ASSEMBLY COMPRISING A PLURALITY OF WATER-COOLED CATHODE CHAMBERS SECURED TO A BASE WHEELED CARRIAGE SLIDABLY MOUNTED ON SAID TABLE MEMBER TO PERMIT SUCCESSIVE IMMERSION IN ELECTROLYTE OF DEPOSITION CATHODES REMOVABLY MOUNTED THEREIN, SEALING ELECTRIC CURRENT TO SAID ASSEMBLIES, MEANS FOR SUPPLYING ELECTRIC CURRENT TO SAID ANODE AND CATHODE, FEEDING MEANS FOR INTRODUING AN ELECTROLYTIC CHARGE INTO SAID CELL, AND MEANS FOR EVACUATING AND FOR INJECTING INERT GAS IN SAID CELL AND CATHODE CHAMBER.