US2848397A

US2848397A - Electrolytic production of metallic titanium

Info

Publication number: US2848397A
Application number: US441324A
Authority: US
Inventors: Lawrence J Reimert; Erastus A Fatzinger
Original assignee: New Jersey Zinc Co
Current assignee: New Jersey Zinc Co
Priority date: 1954-07-06
Filing date: 1954-07-06
Publication date: 1958-08-19
Anticipated expiration: 1975-08-19
Also published as: FR1133552A; LU33710A1; BE539490A; NL96256C; GB777892A

Description

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, 2,848,397 Patented Aug. 19, 1958 Fice ELECTROLYTIC PRODUCTION OF IWETALLIC TITANKUM Lawrence J. Reimert, Schnecksviile, and Erastus A. Fatzinger, Palmerton, Pa., assiguors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application July 6, 1954, Serial No. 441,324 7 Claims. (Cl. 204-64) This invention relates to the electrolytic production of metallic titanium.

In the production of metallic titanium by fused bath electrolysis, the electrodeposited titanium is derived from a' titanium compound present in the molten salt bath. Titanium tetrachloride is a desirable source material for this titanium component of the bath because it can be readily obtained by chlorination of naturally occurring titaniferous materials and can be further purified to the extent requisite for electrolytic production of titanium metal. However, titanium tetrachloride is not only insoluble as such in the molten salt baths which are generally used for such an electrolytic operation but is also a predominantly covalent non-conductor, and consequently great difliculty has been experienced in using titanium tetrachloride for this purpose.

It has been observed heretofore that a molten halide salt bath containing a significant amount of titanium dichloride is capable of readily assimilating titanium tetrachloride by converting it to titanium trichloride. The resulting titanium trichloride is not only soluble in the molten halide bath but can be readily decomposed electrolytically with the resulting cathodic deposition of metallic titanium.

it the production of titanium metal by electrolysis of titanium trichloride formed-in a molten halide salt bath by the aforementioned procedure, it has been found that the chlorine evolved from the anode rapidly oxidizes the lower valent titanium chlorides to titanium tetrachloride with resulting rapid evolution of the insoluble tetrachloride from the molten bath. Consequently, it has been found necessary heretofore to separate the bath into an anolyte and a catholyte by means of a porous diaphragm or metal screen. In typical fused salt electrolysis, no oxidizable ions of multiple valence are present. The only source of inefliciency is reaction between the deposited metal and evolved chlorine gas. It is not difiicult to keep these products separated because simple metal screens, bafiies, or ceramic curtains are adequate for this purpose. In the case of titanium, the lower valence forms are the principal species of the solute and they are readily oxidized by. chlorine gas to the high valence form which has little solubility in the carrier salts; hence, not only must the titanium metal be maintained out of contact with the evolved chlorine but also control over the cell bath must be established in order to minimize damaging mixing of the catholyte with the evolved chlorine. It is obvious that a true porous diaphragm will give maximum separation between catholyte and anolyte while still permitting passage of current through the cell. However, such a diaphragm, if ceramic, adds very appreciably to the cell resistance and commands a substantial portion of the cell voltage. Moreover, such a diaphragm is subject to many complex disruptive forces and, in the end, either becomes conducting or plugged orbecomes mechanically weakened. Metallic diaphragms, or screens, have also been proposed in the fused salt electrolysis of titaniumchloride, the

screen hanging between the anode and cathode and being insulated from each. Such screens do not offer much of a barrier to the circulation of the electrolyte; when used in fused salt electrolysis of titanium halides, they have been used with acceptable efliciency only when electrolysis is carried out at very low solute concentrations. Furthermore, it has been observed that such metallic screens are rapidly corroded in molten salt solutions of titanium chlorides.

In a gesture of curiosity, with the object of ascertaining what would happen when the aforementioned operation was carried out without a diaphragm but under electrolytic conditions which would promote depletion of the titanium component of the bath between the anode and cathode, it was observed that in spite of the apparent depletion of the titanium content of the bath between the anode and the cathode there was an eventual and thereafter continuous deposition of metallic titanium on the surface of the cathode facing away from the anode. As a result of thorough investigation into the factors which promote this result, we have found that several conditions must exist. One of these conditions is that the anode and cathode must be so arranged within the cell that the chlorine evolved at the anode cannot enter to any significant extent the portion of the molten bath adjacent the surface of the cathode facing away from the anode, that is, the distal surface of the cathode. Another condition which we have found essential to obtain the aforementioned result is maintaining direct communication between the body of the bath between the anode and the proximate cathode surface (that is, the cathode surface facing the anode) and the body of the bath adjacent the distal surface of the cathode, while nevertheless minimizing the entry (by circulation or by diffusion, or both) of the titanium chloride component of the latter into the former. Still another condition upon which this result is predicated is the maintenance of an electrolyzing cell voltage which is high enough to effectively deplete the titanium component of the body of molten bath between the anode and the proximate cathode surface but is not so high as to cause decomposition of any of the non-titaniferous components of the bath.

Accordingly, our present invention is directed to the electrolytic production of metallic titanium wherein a chloride of titanium having a valence lower than four is electrolyzed between an anode and a cathode in a molten halide salt bath with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode. Our improvement in this method, which makes possible the production of metallic titanium without the use of any physical barrier in the molten bath between the anode and cathode, comprises (1) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode and sufliciently close to one another to permit electrolytic depletion of the titanium content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of sufliciently small area to retard diffusion of the tita nium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, and (3) effecting electrolysis of the titanium chloride at a voltage high enough to establish and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface as to develop a back electromotive force between the anode and cathode of at least 2.6 volts but insufiicient to effect decomposition of any of the nontitaniferous components of the bath. Under these operating conditions, metallic titanium will be deposited primarily on the distal surface of the cathode at high .current efficiencies in the absence of anyphysical barrier between any significant portion of theproxirnatesurfaces of the anode and cathode. The term physicalbarrier, as used herein and in the claims, means a carrier to the physical movement of the molten salt. Thus, if there should be any desire therefor, a wire screen may be interposed between the anode and cathode, pursuant to our invention provided that the other procedural requirements for the practice of our invention are satisfied.

The molten salt baths which are useful in practicing our 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, we presently prefer to use only the chlorides of these metals. Although an individual halide may be used as a single constituent bath, it is preferred to use a combination of these halides inasmuch as such combinations are characterized by relatively lower melting points than the individual salts. We have found it particularly advantageous, when using a combination of the aforementioned halides, to mix these halides in proportions approximating a eutectic composition. For example, we have used with particularly satisfactory results a eutectic mixture composed of 5 mol percent of sodium chloride, 40 mol percent of potassium chloride and 55 mol percent of lithium chloride, the resulting mixture having a reported melting point of 372 C. but actually melting according to our own observations 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 24 mol percent of barium chloride, 35 mol percent of sodium chloride and 41 mol percent of potassium chloride having a melting point of 552 C. 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 dichloride in such a molten salt bath may be established 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 titaniurn 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 sufiicient to effect reduction of the titanium tetrachloride to alower 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, itspresence in the molten halide salt bath imparts to the bath the'characteristic of readily as- 4 sirnilating titanium tetrachloride when the latter is brought into contact with the bath.

The titanium tetrachloride is advantageously supplied to the bath by maintaining an atmosphere of titanium tetrachloride vapors above but in contact with the molten bath. Although titanium tetrachloride may be introduced into the bath by bubbling it thereinto, we have found that the resulting agitation of the bath is inimicable to the requi ite condition that circulation of the bath components be maintained at a minimum. Regardless of how the titanium tetrachloride is supplied to the bath, the cell atmosphere should be compartmented to maintain separation between this atmosphere and the chlorine which is evolved from the anode. Moreover, the cell should be tightly closed to exclude the ambient atmosphere.

The relative position between the anode and cathode within the molten salt body, in addition to their being not separated by any physical barrier between significant portions of their effective surfaces, should be such that (a) chlorine evolved at the anode will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode, (b) these two body portions of the bath are in direct communication with one another through a passage of sufiiciently small area to retard diffusion of titanium chloride from the body portion of the bath adjacent the distal surface of the cathode into the body portion of the bath between the anode and proximate cathode surface, and (c) the distance between the anode and the proximate cathode surface is sutficiently small to permit the 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 which Fig. 1 is a partial sectional elevation of an electrolytic cell arrangement capable of being used in practicing our invention;

Figs. 2, 3 and 4 are partial sectional elevations of three additional cell arrangements useful in practicing our invention; and

Fig. 5 is a partial sectional elevation of another modification of anode-cathode assembly useful in practicing our invention.

In each of Figs. 1 through 4, the anode and cathode assembly is positioned within a cell 10 containing a molten salt bath the level of which is indicated by the line 11. The anode and cathode arrangement immersed in this bath in the modification shown in Fig. 1 comprises a central anode rod 12 and a surrounding cylindrical cathode 13. The uppermost end of the cathode is joined to a cylindrical noncorrosive material 14 such as a glass tube, although it must be understood that even a metal tube may be used for this purpose provided that it is not readily attacked by either titanium tetrachloride vapors or chlorine gas at elevated temperatures. Electrical connection is made to the cathode through one or more lines 15 which may also be used as a mechanical support for carrying the weight of the cathode suspended in the bath. The anode 12 does not extend as far down into the bath as the cathode 13 so that chlorine evolved at the anode during electrolysis will rise upwardly into the atmosphere above the bath where it will be contained within the cylindrical walls 14 whence it can he withdrawn from the cell. The lower projection of the cylindrical cathode 13 further aids in preventing the entry of evolved chlorine from the portion of the bath identified by the letter A (and comprising the bath between the anode and the proximate cathode surface) into the outer portion of the bath identified by the letter B (and comprising the portion of the bath in contact with the distal surface of the cathode 13).

In the anode-cathode arrangement shown in Fig. 2, which is substantially the same as that shown in Fig. l, the lower extremity of the cathode 13 is provided with an inwardly projecting flange portion 16. This flange portion 16 not only insures containment of the evolved chlorine between the anode 12 and the proximate surface of the cathode 13 but it further restricts the area of the passage through which titanium chloride in the bath portion B can diffuse into the bath portion A.

In the anode-cathode arrangement shown in Fig. 3, the anode comprises a cylinder 17 positioned either close to or immediately adjacent the side walls of the cell 10, and the cathode comprises a cylinder 13 concentrically arranged within and spaced a short distance inwardly from the anode cylinder 17. Although this arrangement assures containment of evolved chlorine within the body portion A of molten bath in contact with the proximate surface of the cathode 13, the relatively large opening at the lower end of the cylindrical cathode 13 requires partial closure in order to hold to a minimum the diffusion of titanium chloride from the body portion B to the body portion A of the bath. Such a partial closure may be provided either by a centrally located disk 18, supported for example by arms 19 dependingfrom the lower end of the cathode 13, or by the same type of inwardly projecting flanges 16 shown in Fig. 2. Either ofthese arrangements effects the desired control over the rate of diffusion of titanium chloride from the body portion B to the body portion A of the bath while nevertheless maintaining direct communication between these two body portions.

The anode-cathode arrangement shown in Fig. 4 comprises substantially flat anode and cathode plates or sheets positioned vertically within the cell 10. Both the anode sheets 20 and the cathode sheets 21 extend nearly the full distance across the cell, and are insulated from the side walls of the cell if they are arranged to make contact with these walls, but both the anode and the cathode sheets terminate above the bottom of the cell with the lower ends of the anode being higher than the lower ends of the cathode. In such an arrangement, each anode 20 is provided with a cooperating pair of cathodes 21 so that with respect to each anode 20 there will be a body portion A of the molten bath positioned between the anode and the proximate surfaces of the cooperating cathodes as well as a body portion B of the molten bath adjacent the distal surface of each cathode 21.

In each of the cell arrangements described hereinbefore the chlorine evolved at the anode leaves the surface of the bath within the confines of the upper cathode walls 14 which thus define a compartment C in the cell atmosphere containing the cell exhaust gas. The portion of the cell atmosphere exterior of this cell exhaust compartment defined by the walls 14 comprises a compartment D into which titanium tetrachloride may be introduced for assimilation by the bath. It will be seen, accordingly, that the titanium tetrachloride is absorbed by surface contact with the body portion B of the bath, that is, by contact with the surface of that portion of the bath in contact with or adjacent the distal surface of each cathode. The body portion A of the bath, on the other hand, is maintained substantially completely depleted of titanium ions by control of the electrolyzing conditions.

The electrolyzing condition which assures the maintenance of titanium-depletion in the body portion A of the molten bath between the anode andthe proximate cathode surface comprises the use of a voltage sufficiently high to strip the body portion A of the bath of its titanium chloride content. We have found that when the body portion A is effectively stripped of its titanium chloride content, thus leaving essentially only the aforementioned eutectic bath composition composed of lithium, sodium and potassium chlorides, the back electromotive force of the cell, when measured across the anode and cathode upon opening of the exterior cell circuit, has a magnitude of 2.6 volts or more when operating with a bath temperature of about 550 C. We have found that a back electromotive force as close tothis lower limit as 2.4 volts is a distinct indication of the presence of substantial amounts of titanium chloride in the body portion A. With back electromotive force values increasing above the aforementioned eifective lower limit of 2.6 volts, current efiiciencies rise from about -85% to about and higher as this voltage rises to about 3.2 volts. As this upper limit is exceeded, and particularly as the back electromotive force reaches about 3.5 volts, decomposition of the non-titaniferous bath components such as the alkali metal chlorides begins to occur. It must be understood that, as appreciated by one skilled in the art of fused salt electrolysis, the maximum back electromotive force will be influenced by the bath composition, by the electrode compositions and by the bath temperature, but in general it can be stated that under most conditions our presently preferred upper limit for the back electromotive force is about 3.4 volts.

When the aforementioned requisite conditions are established and maintained, only a small amount of metal lic titanium is deposited on the proximate surfaces of the cathodes and substantially all of the titanium is deposited electrolytically on the distal cathode surfaces. This result appears to follow from the fact that the body portion A of the molten bath between the anode and proximate cathode surface is substantially depleted of its titanium chloride content and therefore the cell current flows from the anode to the distal surface of each cathode through the direct communication passage between the body portion A and the body portion B of the molten bath. The cross-sectional area of this communication passage between the two body portions A and B may vary considerably provided that it is not so great as to permit a rate of diffusion of titanium chloride from the body portion B into the body portion A at a rate greater than the rate at which titanium chloride can be electrolytically depleted from the body portion A. At the other extreme, a multitude of small openings can be used for the direct communication passage between the body portions A and B. For example, we have obtained wholly satisfactory results by operating under the aforementioned requisite conditions with a cathode composed of a metal screen in the form of a cup 22 so that the bottom of the cup, except for the screen openings, completely closed the bottom of the lowermost extention of the cylindrical cathode wall 13. The titanium deposit formed on the distal surface of the screen cathode is sufficiently porous to permit progressive build-up of metal on this distal surface. The resulting mass of deposited metal between the deposition surface thereof and the screen is not, of course, a physical barrier between the anode and cathode as this term is used herein and in the claims.

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 titanium and nickel, and preferably corrosion-resistant nickel base alloys, are useful in practicing the invention. At the prevailing cell temperature, the aforementioned cathode materials have been found not to contaminate the deposited metallic titanium to any significant degree and may be used in solid or foraminous form.

The practice of our invention may be illustrated by the following specific example:

A Pyrex glass cell having an internal diameter of 2% inches was filled with the aforementioned lithium chloride-potassium chloride-sodium chloride eutectic melt to a depth of about 3 inches and maintained at a temperature of 560 C. The electrode arrangement was that of Fig. 2 with a graphite anode inch in diameter and with a nickel-base alloy cathode having an inside diameter of 1% inches and 1% inches long, the bottom of .7 the cathode being provided with a central aperture /3 inch in diameter. Prior to.electrolysis, a lower titanium chloride concentration of 4.4% calculated as titanium trichloride was established by reacting titanium metal with titanium tetrachloride, and during most of the electrolysis this lower chloride concentration was maintained by adding titanium tetrachloride through the cell atmosphere in balance with the current passed through the cell. Electrolysis was carried out at an impressed voltage ranging from 3.8 to 4.3 volts and with a current ranging from 4.4 to 5.9 amperes. During this interval the back electromotive force, as determined by a high resistance voltmeter, ranged from 2.7 to 3.1 volts. After 5 hours and 20 minutes of operation under these conditions, the titanium tetrachloride feed was stopped and the melt was stripped of lower. titanium chlorides by continued electrolysis at gradually decreasing impressed volt-- age and current. The anode efficiency for the entire run, based on evolved chlorine absorbed in a potassium iodide solution, was 84.8%. Essentially all of the titanium metal was deposited on the distal surface of the cathode.

It will be seen, accordingly, that by following the procedural prescriptions set forth hereinbefore and in the claims, one can effectively establish and control a. high concentration of titanium lower chlorides (generally a mixture of titanium dichloride and trichloride) in the molten bath adjacent the distal surface of the cathode. This high titanium lower chloride content results in a high rate of adsorption by the bath of the titanium tetrachloride in the cell atmosphere thereabove and thus leads to the formation of a coarsely crystalline titanium metal deposit on the cathode. And inasmuch as this titanium metal is deposited predominantly on the distal surface of the cathode in practicing our invention, the electrolysis may be carried out over an extensive period of operation without danger of the cathode deposit interfering with the cell conditions established by the close spacing of the anode and cathode.

We claim:

1. In the electrolytic production of metallic titanium wherein a chloride of titanium having a valence lower than four, and contained in a molten salt bath consisting essentially of at least one halide of the group consisting of alkali metal and alkaline earth metal halides, is electrolyzed in a cell between an anode and a cathode with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode, the improvement which comprises effecting cathodic deposition of metallic titanium in the absence of a physical barrier in the molten bath between the anode and cathode by I (l) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode and sufficiently close to one another to permit electrolytic depletion of the titanium content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of. sufiiciently small area to retard diffusion of the titanium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, (3) effecting electrolysis of the titanium chloride at a voltage high enough to establish and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface as to develop a back electromotive force between the anode and cathode of at least 2.6 volts but insufficient to effect decomposition of any of the nontitaniferous components of the bath, and (4) supplying titanium tetrachloride to the body of molten bath which is in contact with the distal surface of the cathode so as to .maintain asubstantial concentration of said lower valence titanium chloride.

2. In the electrolytic production of metallic titanium wherein a chloride ofititanium having a valence lower than four, .and contained. in a molten salt bath consisting essentially of at least one halide of the group consisting of alkali .rnetaland alkaline earth metal halides, is electrolyzed in a cell between an anode and a cathode with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode, the improvement which comprises effecting cathodic deposition of metallic titanium in the absence of a physical barrier in the molten bath between the anode and cathode by (l) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode and sufficiently close to one another to permit electrolytic depletion of the titanium content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of sufficiently small area to retard diffusion of the titanium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, (3) effecting electrolysis of the titanium chloride at a voltage high enough to establish-and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface as to develop a back electromotive force between the anode and cathode of at least 2.6 volts but not more than about 3.4 volts, and (4) supplying titanium tetrachloride to the body of molten bath which is in contact with the distal surface of the cathode so as to maintain a substantial concentration of said lower valence titanium chloride.

3. In a process for producing titanium from an electrolyte whose solute is at least one compound selected from the-group consisting of TiCl and TiCl and the solvent is a fused salt consisting essentially of at least one halide of a metal selected from the class consisting of alkali and alkaline earth metals, the improvement which comprises electrolyzing a limited portion of the fused electrolyte between an insoluble anode and a. confronting cathode surface, with no physical barrier between said anode and cathode, at a cell voltage of approximately 4 volts, while maintaining a main body of said molten electrolyte in contact with the remote face of said cathode and in direct communication with said limited portion of electrolyte thru a passage of sufficiently small area to retard diffusion of the solute from said main body to said limited portion, whereby the limited portion of electrolyte is depleted of dissolved titanium chloride at a rate greater than the titanium content can be replaced by diffusion from other portions of the fused electrolyte, and titanium is deposited on only the remote face of the cathode.

4. In a process for producing titanium from an electrolyte whose solute is at least one compound selected from the group consisting of TiCl and TiCl and the solvent is a fused salt consisting essentially of at least one halide of a metal selected from the class consisting of alkali and alkaline earth metals, the improvement which comprises establishing an electric potential across a limited portion of the fused electrolyte between an insoluble anode and a confronting cathode surface, with no physical barrier between said anode and cathode, at a cell voltage high enough to establish and maintain such depletion of the solute of the limited portion of the electrolyte between the anode and the confronting cathode. surfaoeas to develop a back electromotive force between the anode and cathode of at least 2.6 volts but not more than about 3.4 volts, while maintaining in contact with the remote face of said cathode a main body of said molten electrolyte having a substantial content of said solute and in direct communication with said limited portion of electrolyte thru a passage of sufficiently small area to retard diffusion of the solute from said main body to said limited portion, whereby the limited portion of electrolyte is depleted of dissolved titanium chloride at a rate greater than the titanium content can be replaced by diffusion from other portions of the fused electrolyte, and titanium is deposited on only the remote face of the cathode.

5. In the electrolytic production of metallic titanium wherein a chloride of titanium having a valence lower than four, and contained in a molten salt bath consisting essentially of at least one halide of the group consisting of alkali metal and alkaline earth metal halides, is electrolyzed in a cell between an anode and a cathode with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode, the improvement which comprises effecting cathodic deposition of metallic titanium in the absence of a physical barrier in the molten bath between the anode and cathode by (1) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface Without entering thevbody of molten bath adjacent the distal surface of the cathode and sufficiently close to one another to permit electrolytic depletion of the titanium content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of sufficiently small area to retard diffusion of the titanium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, (3) effecting electrolysis of the titanium chloride at a voltage high enough to establish and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface but insufficient to effect decomposition of any of the non-titaniferous components of the bath, and (4) supplying titanium tetrachloride to the body of molten bath which is in contact with the distal surface of the cathode so as to maintain a substantial concentration of said lower valence titanium chloride.

6. In the electrolytic production of metallic titanium wherein a chloride of titanium having a valence lower than four and contained in a molten salt bath consisting essentially of at least one halide of the group consisting of alkali metal and alkaline earth metal halides is electrolyzed in a cell between an anode and a cathode with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode, the improvement which comprises effecting cathodic deposition of metallic titanium predominantly on that surface of a metallic screen cathode which is distal with respect to the anode by (1) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode and sufficiently close to one another to permit electrolytic depletion of the titanium content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of sufficiently small area to retard diffusion of the titanium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, (3) effecting electrolysis of the titanium chloride at a voltage high enough to etablish and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface but insufficient to effect decomposition of any of the non-titaniferous components of the bath, and (4) supplying titanium tetrachloride to the body of molten bath which is in contact with the distal surface of the cathode so as to maintain a substantial concentration of said lower valence titanium chloride.

7. In the electrolytic production of metallic titanium wherein a chloride of titanium having a valence lower than four and contained in a molten salt bath consisting essentially of at least one halide of the group consisting of alkali metal and alkaline earth metal halides is electrolyzed in a cell between an anode and a cathode with the resulting deposition of metallic titanium on the cathode and evolution of chlorine gas at the anode, the improvement which comprises effecting cathodic deposition of metallic titanium predominantly on that surface of a metallic screen cathode which is distal with respect to the anode by (1) establishing and maintaining the relative position between the anode and cathode within the cell such that the evolved chlorine will rise in the body of molten bath between the anode and the proximate cathode surface without entering the body of molten bath adjacent the distal surface of the cathode and suificiently close to one another to permit electrolytic depletion of the titanitun content of the bath therebetween at a rate faster than this titanium content can be replaced by diffusion from other portions of the bath, (2) maintaining the body of molten bath between the anode and the proximate cathode surface in direct communication with the body of molten bath adjacent the distal surface of the cathode through a passage of sufliciently small area to retard diffusion of the titanium chloride from the bath adjacent the distal surface of the cathode into the bath between the anode and proximate cathode surface, (3) effecting electrolysis of the titanium chloride at a voltage high enough to establish and maintain such depletion of the titanium component of the bath between the anode and the proximate cathode surface but insufficient to effect decomposition of any of the non-titaniferous components of the bath, and (4) bubbling titanium tetrachloride into the body of molten bath which is in contact with the distal surface of the cathode so as to maintain a substantial concentration of said lower valence titanium chloride.

References Cited in the file of this patent FOREIGN PATENTS 682,919 Great Britain Nov. 19, 1952

Claims

1. IN THE ELECTROLYTIC PRODUCTION OF METALLIC TITANIUM WHEREIN A CHLORIDE OF TITANIUM HAVING A VALENCE LOWER THAN FOUR, AND CONTAINED IN A MOLTEN SALT BATH CONSISTING ESSENTIALLY OF AT LEAST ONE HALIDE OF THE GROUP CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL HALIDES, IS ELECTROLYZED IN A CELL BETWEEN AN ANODE AND A CATHODE WITH THE RESULTING DEPOSITION OF METALLIC TITANIUM ON THE CATHODE AND EVOLUTION OF CHLORINE GAS AT THE ANODE, THE IMPROVEMENT WHICH COMPRISES EFFECTING CATHODIC DEPOSITION OF METALLIC TITANIUM IN THE ABSENCE OF A PHYSICAL BARRIER IN THE MOLTEN BATH BETWEEN THE ANODE AND CATHODE BY (1) ESTABLISHING AND MAINTAINING THE RELATIVE POSITION BETWEEN THE ANODE AND CATHODE WITHIN THE CELL SUCH THAT THE EVOLVED CHLORINE WILL RISE IN THE BODY OF MOLTEN BATH BETWEEN THE ANODE AND THE PROXIMATE CATHODE SURFACE WITHOUT ENTERING THE BODY OF MOLTEN BATH ADJACENT THE DISTAL SURFACE OF THE CATHODE AND SUFFICIENTLY CLOSE TO ONE ANOTHER TO PERMIT ELECTROLYTIC DEPLETION OF THE TITANIUM CONTENT OF THE BATH THEREBETWEEN AT A RATE FASTER THAN THIS TITANIUM CONTENT CAN BE REPLACED BY DIFFUSION FROM OTHER PORTIONS OF THE BATH, (2) MAINTAINING THE BODY OF MOLTEN BATH BETWEEN THE ANODE AND THE PROXIMATE CATHODE SURFACE IN DIRECT COMMUNICATION WITH THE BODY OF MOLTEN BATH ADJACENT THE DISTAL SURFACE OF THE CATHODE DIFFUSION OF THE TITANIUM CHLORIDE FROM THE BATH ADJACENT DIFFUSION OF THE TITANIUM CHLORIDE FROM THE BATH ADJACENT THE DISTAL SURFACE OF THE CATHODE INTO THE BATH BETWEEN THE ANODE AND PROXIMATE CATHODE SURFACE, (3) EFFECTING ELECTROLYTIS OF THE TITANIUM CHLORIDE AT A VOLTAGE HIGH ENOUGH TO ESTABLISH AND MAINTAIN SUCH DEPLETION OF THE TITANIUM COMPONENT OF THE BATH BETWEEN THE ANODE AND THE PROXIMATE CATHODE SURFACE AS TO DEVELOP A BACK ELECTROMOTIVE FORCE BETWEEN THE ANODE AND CATHODE OF AT LEAST 2.6 VOLTS BUT INSUFFICIENT TO EFFECT DECOMPOSITION OF ANY OF THE NONTITANIFEROUS COMPONENTS OF THE BATH, AND (4) SUPPLYING TITANIUM TETRACHLORIDE TO THE BODY OF MOLTEN BATH WHICH IS IN CONTACT WITH THE DISTAL SURFACE OF THE CATHODE SO AS TO MAINTAIN A SUBSTANTIAL CONCENTRATION OF SAID LOWER VALENCE TITANIUM CHLORIDE.