US2892764A

US2892764A - Production of titanium metals

Info

Publication number: US2892764A
Application number: US729595A
Authority: US
Inventors: Earl W Andrews
Original assignee: New Jersey Zinc Co
Current assignee: New Jersey Zinc Co
Priority date: 1958-04-21
Filing date: 1958-04-21
Publication date: 1959-06-30
Anticipated expiration: 1976-06-30
Also published as: BE577842A

Description

June 30, 1959 E. W. ANDREWS PRODUCTION OF TITANIUM METALS Filed April 21, 1958 JNVENTOR.

Earl W. Andrews (2w 2;; Maximum ATTORNEYS United States Patent PRODUCTION OF TITANIUM METALS Earl W. Andrews, Slatington, Pa., assignor to The New Jersey Zinc Company, New York, N.Y., a corporation 'of New Jersey Application April 21, 1958, Serial No. 729,595

2 Claims. 01. 204-64) This invention'relates to the production of metallic titanium and, more particularly, to a method in which Jitanium metal is electrodeposited from a fused salt bath.

In the copending application ofReimert et al., Serial No.,44l,324, filed July 6, 1954, now Patent No. 2,848,397,

1 there is described a method of operating a fused salt bath electrolyticwcell for the production of metallic titanium -.in such manner that the titanium is deposited on the surface of the cathode facing away from, or distal with respect to, the anode.

This result is achieved, pursuant to the Reimert et 211. method, by (l) supplying the tita- 1 nifer'ous 'source material, titanium tetrachloride, to the portion of the cell bath which is adjacent this distal surface of the cathode, (2) providing a communicating pasretard diffusion of titanium ions from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface,:and (3) maintaining a cell voltage sufficient to maintain depletion of titanium ions in the portion of the bath between the anode and proximate cathode surface such as to establish a back electromotive force within the range of about 2.6 to 3.4 volts between the anode and cathode. This operation is characterized by the fact that the cell produces metallic titanium with high current efficiency and without any physical barrier, such as a diaphragm, between the anode and cathode.

The fused salt bath used in the process of the aforesaid application comprises one or more alkali metal or alkaline earth metal halides in admixture with ionizable titanium compounds, and the titanium tetrachloride is introduced into the atmosphere above the fused salt bath, or directly into the portion of the fused salt bath adjacent the distal surface of the cathode. Titanium tetrachloride is for all practical purposes insoluble in the fused salt bath. How-'' ,ever, the lower chlorides of titanium, namely titanium dichloride and titanium tn'chloride, are quite soluble in the fused salt bath. Moreover, titanium tetrachloride will react with tatanium dichloride to form titanium trichloride, and as a consequence the titanium tetrachloride supplied to the bath or to the atmosphere over the bath reacts with the titanium dichloride present in the bath and thereby enters or dissolves therein in the form of titaniumtrichloride. The electrolysis of the bath reduces the titanium trichloride to the dichloride and reduces:

some of the dichloride to metallic titanium which deposits on the cell cathode.

Some of the dichloride thus formed reacts with a further amount of titanium tetrachloride to form additional titanium trichloride which replaces the titanium content of the bath deposited at the cathode.

"2,892,764 Patented June 30, 1959 adjacent the surface of the fused salt bath in a manner 'of the bath available for electrolytic deposition on the proximate surface of the cathode (i.e. the surface of the cathode facing the anode). Moreover, in order to maintain the portion of the fused salt bath between the anode and the cathode substantially free of titanium ions it is necessary to restrict communication between this portion of the bath and the portion thereof disposed adjacent the distal surface of the cathode so that diffusion of titanium ions from the latter portion of the bath into the former will be retarded as described in the aforesaid application. Accordingly, the cathode, which serves to divide the fused salt bath into the said two portions, is formed for the most part from sheet material impervious to the fused salt bath, the cathode however being also provided with small openings or pervious sections which permit a limited amount of communication between the said two portions of the bath.

Although the portion of the bath between the anode and the cathode is maintained substantially free of titanium ions during most of the electrolysis it has been found impossible in practice to prevent the deposition of a slight amount of metallic titanium on the proximate surface of the cathode, especially during the initial phase of the electrolysis when the portion of the fused bath between the anode and the cathode is being electrolytically depleted of any titanium ions originally present therein. Moreover, even though the fused salt bath is initially free of titanium ions, metallic titanium willdeposit as the result of some unknown mechanism at the interface of the cathode, the substantially titanium-free salt bath and the titanium tetrachloride-containing atmosphere. The actual amount of titanium deposited on the proximate surface of the cathode would ordinarily be of no significance in the successful operation of the process of the aforesaid application. However, it has been found that once metallic titanium commences to deposit on the proxirnate surf-ace of the cathode at or adjacent the surface level of the fused salt electrolyte, the deposit builds up very rapidly so that within a relatively short time the titanium deposit extends across the surface of the electrolyte and makes electrical contact with the cell anode or' with the chlorine dome associated with the anode. As a consequence of this bridging across of the titanium deposit from the proximate surface of the cathode to the chlorine dome or cell anode, the electrolytic operation must be prematurely interrupted.

As a result of an investigation into the cause of this rapid build-up of an undesirable titanium deposit on the proximate surface of the cathode adjacent the surface level of the fused salt bath, I have found that once titanium metal is allowed to deposit at this point on the cathode titanium tetrachloride in the cell atmosphere reacts with the metallic titanium deposit to form titanium dichloride which immediately reacts with a further amount of titanium. tetrachloride to form titanium trichloride. The titanium dichloride and trichloride, thus formed are dissolved in the bath adjacent the proximate .surface of the cathode and adjacent the surface level of the fused salt bath itself so'that as a result of the electrolyzing current flowing between the anode and the cathode the aforementioned undesirable deposit of metallic titanium is rapidly built up on the proximate surface of the cathode adjacent the surface level of the fused salt bath. My investigation further revealed that the undesirable build-up of metallic titanium can be eliminated by maintaining the cell atmosphere above the portion of the fused salt bath between the anode and the cathode free 'of titanium tetrachloride so that even though a trifling amount of metallic titanium may deposit on the proximate surface of the cathode, there will be no titanium tetrachloride available to react with this metallic titanium and thereby enter this portion of the bath in the form of titanium dichloride. Furthermore, I have discovered that the cell atmosphere above the aforesaid portion of the rate the cell atmosphere into two portions one of which contains tetrachloride vapors and the other of which does not.

Accordingly, my improvement in the process of making metallic titanium in which an electrolyzing current is passed between an anode and a cathode immersed in a fused salt bath composed essentially of at least one of the alkali metal and alkaline earth metal halides and containing titanium ions having a valence of less than 4, in which the cathode comprises at least one imperforate portion and at least one perforate portion, said imperfo {rate portion substantially separating the portion of the fused salt bath disposed between the cathode and the anode from the remainder of said bath and said perforate portion of the cathode providing limited communication .laetween the said two portions of the bath, in which titanium tetrachloride is supplied to the portion of the -pbath adjacent the surface of the cathode distal With respect to the anode in which a chlorine dome is provided adjacent the anode surrounding the upper portion thereof and adapted to collect the halogen gas evolved at the anode, and in which the portion of the bath between the anode and the proximate cathode surface is maintained sufiiciently depleted of titanium ions so that substantially all of the metallic titanium is deposited on said distal ,surface of the cathode comprises: extending the imperforate portion of the cathode upwardly from the surface of the fused salt bath to the cover of the electrolytic cell whereby the gaseous atmosphere within the electrolytic cell is divided into two non-communicating portions.

The molten salt baths which are useful in practicing my invention comprise one or more of the halides of the alkali metals and alkaline earth metals. Thus, the chlorides, bromides, iodides and fluorides of sodium, potassium and lithium as well as the same halides of calcium, magnesium, barium and strontium may be used with advantage. However, in the interest of simplifying the recovery of the halogen which is liberated at the anode during electrolysis, I presently prefer to use only the chlorides of these metals. Although an individual halide may be used as a single constituent bath, I now prefer to use a combination of these halides inasmuch as such combinations are characterized by relatively lower melting points than the individual salts. It is particularly advantageous, when using a combination of the aforementioned halides, to mix these halides in proportions approximating a eutectic composition in order to obtain baths with low melting points. For example, I have used with particu larly satisfactory results a eutectic mixture composed of 5 mol percent of sodium chloride, 40 mol percent of potassium chloride and 55 mol percent of lithitun chloride, the resulting mixture having a reported melting point of 372 C. but actually melting at a temperature of about 345 C. Other useful eutectic mixtures are represented by the mixture composed of 48.5 mol percent of sodium chloride and 51.5 mol percent of calcium chloride having a melting point of 505 C. and by the mixture composed of 24mol percent of barium chloride, 35 mol percent 7 of sodium chloride and 41 mol percent of potassium chloride having a melting point of 552 C. 7 Of course, as in all other molten salt electrolytic methods for the production of metallic titanium, the bath should be as completely anhydrous as possible and should be compounded of salts of high purity.

A content of titanium ions having a valence of less than four, such as titanium dichloride, may be established in such a molten salt bath by any one of a number of procedures. For example, titanium dichloride from an extraneous source may be introduced directly into the bath. On the other hand, the titanium dichloride may be formed in situ in the bath by dispersing finely divided metallic titanium throughout the bath and by then bubbling titanium tetrachloride into the bath so that, as a result of the reaction between the metallic titanium and the titanium tetrachloride, titanium dichloride is formed in the bath. The lower valence titanium chloride content of the bath may also be established by continuously exposing the bath to a titanium tetrachloride atmosphere while maintaining an impressed cell voltage either below or above the decomposition voltage of one or more components of the carrier salt bath but suflicient to effect reduction of the titanium tetrachloride to a lower valence titanium chloride. The dichloride can also be formed in the bath by introducing the trichloride into the bath, or forming it in situ by the aforementioned electrolysis, and by thereafter electrolytically reducing the trichloride to the dichloride. Regardless of the source of the titanium dichloride, its presence in the molten halide salt bath in amount of at least about 0.1% by weight of the bath, and preferably about 3% by weight, imparts to the bath the characteristic of readily assimilating titanium tetrachloride when the latter is brought into contact with the bath.

The titanium tetrachloride is advantageously supplied to the bath by bubbling the tetrachloride into the bath, or by maintaining an atmosphere of titanium tetrachloride vapors above but in contact with the molten bath. Regardless of how the titanium tetrachloride is supplied to the bath, the cell atmosphere should be compartmented to maintain separation between the tetrachloride-containing atmosphere above the bath adjacent the distal surface of the cathode and the tetrachloride-free atmosphere above the bath adjacent the proximate surface of the cathode. Moreover, the cell should be tightly closed to exclude the ambient atmosphere. 7

The cell electrodes should, of course, be constructed of material which will not introduce extraneous elements into the fused bath. Thus, a nonmetallic anode such as graphite or carbon should be used, graphite having been found in practice to be wholly suitable for this purpose. Cathodes of nickel, and preferably of corrosion-resistant nickel base alloys, are useful in practicing the invention. As noted the cathode comprises at least one impervious portion and at least one pervious portion which together serve to substantially separate the fused bath into two portions and to retard diffusion of titanium ions from one of said portions of the bath to the other. Moreover, in accordance with the present invention the imperforate portion of the cathode extends upwardly to the air-tight cover of the electrolytic cell and thus serves to separate the tetrachloride-containing atmosphere of the cell from the tetrachloride-free atmosphere of the cell as previously described. At the prevailing cell temperature, the aforementioned anode and cathode materials have been found not to contaminate the fused bath or the deposited metallic titanium to any significant degree.

The relative position between, and the arrangement of, the anode and cathode within the molten salt body should be such that (a) chlorine evolved at the anode will rise in the body of molten bath without entering the body of molten bath adjacent the distal surface of the cathode, (b) the titanium tetrachloride introduced into the cell adjacent the distal surface of the cathode Will be prevented from entering the cell atmosphere above the bath adjacent the proximate surface of the cathode, (c) the body of molten bath between the anode and the proxithe bath between these surfaces, is sufliciently small to permit electrolytically induced depletion of the titanium content of the molten bath between these surfaces.

A number of arrangements of anode. and cathode will assure these conditions, and a variety of such arrangements is shown in the drawings in the aforementionedReimert et al. application However, a presently preferredcell arrangemeht for practicing the invention is shown in the accompanying drawing in which the single figure is a partial sectional elevation of the cell.

As shown in the drawing, the electrolytic cell 1 is provided with a gas-tight cover 2 through which extends an inlet pipe 3 for introducing titanium tetrachloride vapor into the cell and an outlet pipe 4 for withdrawing gas from the cell atmosphere. The cell 1 contains a fused salt bath 5 in which a cylindrical cathode 6 is partially immersed. The cylindrical cathode is closed at its lower end by means of an impervious bottom wall 7 and is connected at its upper end to the cover 2 of the cell. The cylindrical cathode can be attached or secured to the cover 2 by any suitable means, such as by bolting or welding it to the cover or by providing the upper edge of the cathode with a lip portion 8 which rests on the cover 2 as shown in the drawing. The cylindrical side wall portion 9 of the cathode is advantageously composed of impervious sheet material having large openings 10 provided at intervals throughout its surface and having a lining of screen material 11 secured to the inner surface of the side wall portion, the cathode assembly thus separating the fused salt bath 5 into an inner body portion A and a main body portion B. Furthermore, in accordance with the present invention the impervious side wall portion 9 of the cathode extends upwardly to the cover 2 of the electrolytic cell so that the cell atmosphere is divided into an inner portion C and an outer portion D, the inner portion C of the cell atmosphere being disposed above the inner portion A of the fused salt bath and the outer portion D of the cell atmosphere being disposed above the main body portion B of the fused salt bath. The impervious bottom wall and side wall portion of the cathode are constructed of sheet metal composed of a corrosion-resistant nickel-base alloy, and the pervious screen 11 of the cathode is advantageously constructed of Dutch weave wire mesh screen of the same corrosionresistant metal, the screen advantageously having 14 mesh per inch in one direction and 120 mesh per inch in the other direction. Other wire screens ranging from as coarse as 8 mesh to as fine as calendered wire filter cloth can be used effectively in the cathode construction. The cathode assembly is connected by suitable means to a source of electrolyzing current.

The anode assembly for the electrolytic cell comprises a silica chlorine dome 12 extending downwardly into the interior of the cathode assembly, the lower extremities of the dome 12 being immersed in the fused salt bath 5. The dome 12 is secured to a graphite anode base 13 which is provided with ports 14 and a depending anode section 15. The chlorine dome 12 and the anode base 13 together define a compartment E within the cell directly above the depending anode section 15 which is part of the anode base. Chlorine gas evolved at the anode section 15 rises up through the bath and enters the compartment E from whence it is withdrawn through the ports 14 and the chlorine effluent tube 16. The cell cover 17 over the anode-cathode assembly is also provided with a gas inlet 18 and gas outlet 19 for argon which is used to sweep chlorine out of portion C of the cell atmosphere.

Titanium tetrachloride advantageously admixed with an inert carrier gas such as argon is introduced into the lower portion of the main body portion B of the fused bath through the inlet pipe 3. The tetrachloride thus introduced reacts'with the lower valent titanium ions present in the main body portion B of the fused salt bath and thereby enters this portion of the bath in the form of titanium trichloride. Any titanium tetrachloride that is not thus assimilated by the fused salt bath and the inert carrier gas, if any, rise upward through the bath and enter the outer portion D of the cell atmosphere from whence this excess tetrachloride and carrier gas are withdrawn through the outlet pipe 4. Asa result it will be seen that the outer portion D of the cell atmosphere contains titanium tetrachloride in gaseous form. However, the impervious side wall portion 9 of the cathode which extends from the surface of the fused salt bath 5 to the cover 2 of the cell prevents any titanium tetrachloride present in the portion D of the cell atmosphere from entering the portion C of the cell atmosphere disposed about the inner body portion A of the fused salt bath. As a consequence there is no titanium tetrachloride in the cell atmosphere above the portion A of the bath adjacent the proximate surface of the cell cathode available to react with the fused salt bath or with an incipient metallic titanium deposit on the proximate surface of the cathode adjacent the surface level of the bath. As a result, the inner body portion A of the bath between the anode and the cathode remains substantially free of titanium ions adjacent the surface level of the bath, and the undesirable build-up of a metallic titanium deposit at this point on the proximate surface of the cathode is prevented.

From the foregoing description of my invention it will be seen that I have made an important contribution to the art of electrolytically producing titanium metal.

I claim:

1. In the method of producing metallic titanium in which an electrolyzing current is passed between a fused halide bath contained in a covered electrolytic cell, said bath being composed essentially of at least one of the alkali metal and alkaline earth metal halides and containing titanium ions having a valence of less than 4, in which the cathode comprises at least one perforate portion and at least one imperforate portion, said perforate portion of the cathode providing communication between the portion of the fused halide bath disposed between the cathode and the anode and the remainder of said bath, in which titanium tetrachloride is supplied to the portion of the bath adjacent the surface of the cathode distal with respect to the anode, in which a chlorine dome is provided adjacent the anode surrounding the upper portion thereof and adapted to collect the halogen gas evolved at the anode, and in which the portion of the bath between the anode and the proximate cathode surface is maintained sufficiently depleted of titanium ions so that substantially all the metallic titanium is deposited on said distal surface of the cathode, the improvement which comprises extending the imperforate portion of the cathode upwardly from the surface of the fused salt bath to the cover of the cell whereby the cell atmosphere above the portion of the bath adjacent the distal surface of the cathode is separated from the cell atmosphere above the portion of the bath adjacent the proximate surface of the cathode.

2. In the method of producing metallic titanium in which a fused halide bath composed essentially of at least one of the alkali metal and alkaline earth metal halides and containing titanium ions having a valence of less than 4 is disposed in a covered electrolytic cell, in which an electrolyzing current is passed between an anode and a cathode immersed in said bath with the resulting deposition of metallic titanium on said cathode, in which the cathode comprises at least one perforate portion and at least one imperforate portion, said imperforate portion of the cathode substantially separating the portion of the fused salt bath disposed between the cathode and the anode from the remaining portion of said bath and said perforate orfiei ofthe' cathode 7 of the cathode distal with respect to the anode, in which a chlorinedonie is provided adjacent the anode surrounding the upper portion thereof and adapted to'collect' the halogen gas evolved at the anode, and in which the portion of the bath between the anode and the proximate cathode surface is maintained sufliciently depleted of titanium ions so that substantially all the metallic titanium is deposited on said distal surface of the cathode, the

" improvementwhich comprises extending the imperforate portion of thecathode'up'wardly from the surface of the fused salt bath to the cover of the electrolytic cell whereby the cell atmosphere abovethe portion of the bath adjacent the distal surface of the cathode is separated from the portion of the cell atmosphere above'the bath adjacent the proximate surface of the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,848,397 Reimert et a1. Aug. 19, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2,892,764 June 30, 1959 Earl W a Andrews It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 18, for "about the inner body portion A" read above the inner body portion A e Signed and sealed this 10th day of November 1959.

(SEAL) Attest:

KARL HQ AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims

1. IN THE MEHTOD OF PRODUCING METALLIC TITANIUM IN WHICH AN ELECTROLYZING CURRENT IS PASSED BETWEEN A FUSED HALIDE BATH CONTAINED IN A COVERED ELECTROLYTIC CELL, SAID BATH BEING COMPOSED ESSENTIALLLY OF AT LEAST ONE OF THE ALKALI METAL AND ALKALINE EARTH MEAL HALIDES AND CONTAINING TITANIUM IONS HAVING A VALENCE OF LESS THAN 4, IN WHICH THE CATHODE COMPRISES AT LEAST ONE PERFORATE PORTION ANS AT LEAST ONE IMPEROFRATE PORTION, SAID PERFORATE PORTION OF THE CATHODE PROCIDING COMMUNICATION BETWEEN THE PORTION OF THE FUSED HALIDE BATH DISPOSED BETWEEN THE CATHODE AND THE ANODE AND THE REMAINDER OF SAID BATH, IN WHICH TITA(IUM TETRACHLORIDE IS SUPPLIED TO THE PORTION OF THE BATH ADJACENT THE SURFACE OF THE CATHODE DISTAL WITH RESPECT TO THE ANODE, IN WHICH A CHLORINE DOME IS PROVIDED ADJACENT THE ANODE SURROUNDING THE UPPER PORTIO THEREOF AND ADPATED TO COLLECT THE HALOGEN GAS EVOLVED AT THE ANODE, AND IN WHICH THE PORTION OF THE BATH BETWEEN THE ANODE AND THE PROXIMATE CATHODE SURFACE IS MAINTAINED SUFFICIENTYL DEPLETED OF TITANIUM IONS SO THAT SUBSTANTIALLY ALL THE METALLIC TITANIUM IS DEPOSITED ON SAID DISTAL SURFACE OF TRH CATHODE, THE IMPROVEMENT WHICH COMPRISES EXTENDING THE IMPERFORATE PORTION OF THE CATHODE UPWARDLY FROM LTHE SURFACE OF THE FUSED SALT BATH TO THE COVER OF THE CELL WHEREBY THE CELL ATMOSPHERIC ABOVE THE PORTION OF THE BATH ADJACENT THE DISTAL SURFACE OF THE CATHODE IS SEPARATED FROM THE CELL ATMOSPHERE ABOVE THE PORTION OF THE BATH ADJACENT THE PROXIMATE SURFACE OF THE CATHODE.