US2741588A

US2741588A - Electrolytic production of titanium metal

Info

Publication number: US2741588A
Application number: US249958A
Authority: US
Inventors: Marshall B Alpert; Powell Robert Lee
Original assignee: Nat Lead Co
Current assignee: NL Industries Inc
Priority date: 1951-10-05
Filing date: 1951-10-05
Publication date: 1956-04-10
Anticipated expiration: 1973-04-10
Also published as: GB712742A; FR1064126A

Description

April 10, 1956 ALPERT ET AL 2,741,588

ELECTROLYTIC PRODUCTION OF TITANIUM METAL Filed Oct. 5, 1951 3 Sheets-Sheet 1 Fig. l. l

cecocooboo QOQOOOQ l x 'l INVENTORS Marshall B. Alpert BY Robert L. Powell April 10, 1956 M. B. ALPERT ETAL 2,741,588

ELECTROLYTIC PRODUCTION OF TITANIUM METAL Filed Oct. 5, 1951 3 Sheets-Sheet 2 INVENTORS Marshall B. Alpert Robert L. Powell than 0.1 in proximity to the solubilization cathode, and

it is desirable to maintain a current density in amperes per square centimeter on the solubilization cathode no more than the numerical molality of the titanium trichloride.

It has been found that when higher concentrations of titanium values in the salt melt are present in the vicinity of the solubilization cathode, current may be passed through at an increased rate and the capacity of the cell thereby improved. It has been found quite convenient to operate at a titanium dichloride molality of about 10. Besides increasing the capacity of the cell, the higher current densities are advantageous in another way, that is, they have the effect of heating the cell, and if the cell is sufiiciently large and the current density sufiiciently high, no other means for supplying heat need be used.

It is not difiicult to maintain the concentrations of both titanium dichloride and titanium trichloride within the limitations given above. It is, of course, possible to choose and maintain a salt bath composition which meets the limitations both for electrolyte in proximity with the solubilization cathode and for electrolyte in proximity with the deposition cathode. It is often desirable from an operational standpoint, however, to operate in such a manner that the electrolyte in the vicinity of the solubilization cathode is of a different concentration with respect to the reduced titanium values than the electrolyte near the deposition cathode. This may be accomplished in many Ways. One such method which has been proven to be satisfactory is to divide the cell into two sections, each'section having a cathode. It is convenient to place a porous diaphragm as the boundary between the two sections. In this type of cell construction, the soluble titanium values formed at the solubilization cathode pass through the diaphragm and are reduced to titanium metal and deposited on the deposition cathode in the second chamber. The action of the diaphragm will cause the concentration of the titanium values in the second chamber to be maintained considerably lower than the concentration of titanium values in the first chamber. Another method of obtaining the desirable differential between the titanium concentrations in proximity to the two cathodes is to provide a solid wall between the two cathodes to form two separate chambers and to pump a small portion of the solution from the solubilization cathode chamber into the second chamber containing the deposition cathode. Another type of apparatus which may also be employed provides a single chamber containing both cathodes but having the cathodes spaced at a considerable distance from oneanother so that the difiusion of titanium values formed at the solubilization cathode is slow enough to provide a low concentration of titanium values at the deposition cathodes.

In order to define moreclearly the process of the instant invention the following drawings are presented in which Fig. 1 shows a vertical cross section of an electrolytic cell in which titanium metal may be produced continuously,

Fig. 2, a horizontal cross section of the cell shown in Fig. 1 cut across line 2-2,

Fig. 3, a perspective view of another type of electrolytic cell partially cut out.

Fig. 4, a frontview of the cell shown in Fig. 3 partially cut out, and

Fig. 5, a cross section of the cell shown in Fig. 4 cut along line 5-5. I

Referring now to Fig. 1 an electrolytic cell is placed in a suitable furnace which is provided with heating means such as gas burners 11. Disposed within the heated zone is cell container 12 which is made from corrosion-resistant material such as fused impervious silica and preferably protected externally by a metallic sheath 13, for instance of stainless steel or other metal resistant to the heat efiects involved. The cell container 12 is filled, or partially filled with electrolyte 14 in which are suspended

cathodes

16 and 17 which may preferably comprise elongated plates of a noble metal such as tantalum. Cathode 16 is the solubilization cathode while 17 is the deposition cathode. The anode 13 may be formed of graphite rods, and is also submerged in the electrolyte. The cathodes are separated from the anode by a porous diaphragm 19, which surrounds the immersed portion of the anode 18 to form an anode compartment.

in this particular design an additional porous diaphragm 2t surrounds the deposition cathode 17. Cover 21 is provided to enclose the top of the cell and contains means 22 for admission of inert gas, such as argon or helium to protect the surface of the molten electrolyte. The space 7 above the anode compartment is provided with means 23 as pipes for carrying off the chlorine released at the anode. Titanium tetrachloride is added preferably through tube 24 which terminates in the cell at a point near solubilization cathode 16. The upper portion of the diaphragm 19 which extends above the surface of the electrolyte may be constructed of non-porous material, e. g. an impervious sleeve 25 which will act as a nonporous top section on the diaphragm if desired in order to insure complete separation of the chlorine gas evolved during the entire electrolytic process.

Fig. 2 illustrates a horizontal cross section of the cell shown in Fig. 1 cut along line 22.

In operating this cell the titanium tetrachloride is substantially completely reduced to titanium dichloride at cathode 16. The titanium values produced pass through the second mentioned porous diaphragm 20 and are reduced and deposited as titanium metal on deposition cathode 17.

Another type of cell which may also be used with equal efiiciency is the type shown in Fig. 3. In'this type of cell the cell container 31 is also placed in a gas furnace. The electrolyte 32 is placed in the container and anode 33 and two

cathodes

34 and 35 are submerged in the electrolyte. Cathode 34 is the solubilization cathode while cathode 35 is the deposition cathode. The anode is preferably placed between the two cathodes. In order to separate the anode from the two cathodes,

porous diaphragms

36 and 37 are inserted. In operating this cell titanium tetrachloride is introduced through tubes 38 which terminate near the solubilization cathode 34. The melt containing the titanium values formed by cathode 34 is pumped through passageway 39 by pump 40 from the chamber surrounding cathode 34 into the chamber. surrounding deposition cathode 35. The titanium values arre reduced in the second chamber and deposited as titanium metal on deposition cathode 35. The solution partly depleted of titanium values in the second chamber is pumped back into the first mentioned cathode chamber. Fig. 4 is a front view of the same cell shown in Fig. 3, and is given to supplement the description of Fig. 3. Fig. 5 is a horizontal cross-section of the cell shown 1]] Figs. 3 and 4, taken along the line 55 of Fig. 4, and shows in addition to the features illustrated in Figs. 3 and 4, pump 42 and passageway 43 by means of which the solution depleted of titanium values is pumped back from the chamber surrounding deposition cathode 35 into the chamber surrounding solubilization cathode 34.

The type of electrolyte used in carrying out the process of this invention must be chosen to accomplish certain desired efiects. The constituents of the electrolyte should be selected with a view to melting temperature, corrosive effects, compatability and appropriate electrical characteramass U a. 13 P i i l f is a mixture of strontium chloride and sod'ium chloride. It is particularly advantageous to employ a mixture of 73 parts of strontium chloride and 2 7 parts of sodium i bYjFjigHt-r 5 53 .3 .5 m t Phi of a 560 C. and in addition appearslto afie'ct beneficial of the depositedtitanium me at.

he iarh as' s us d, mm; @61 may e: eiis n c ed o rr ws els fl nclnec d five mat a hi h @33 m ieed El mp mel a d. t s v s .O h sall tbath and permit the now o fi'ons but retard .c'onfvectiqn'al mirdng of difier ent portions of the melt. Satis 55? Ir m sh 've renob n by fli 1 of a l nt i 1mm p Is dia hr Di hra m c a pablepf passing particles of a maximumsize between one micron and ZQ mi'crQns in aqueous media havebeen ar ti cula'rly' successfully employed in the electrolytic process.

ln A order tq' aecotnplish the production of titanium n 'etalon a continuous basis, it is desirable to add current it 56 t a s r mo f taniumit s de ntroliF d. 9 55 1. 9 h cthdds i li d iit ie 11. i 1

s lw d i t qdu ed a ut. y. be v h 0 a 1 ab i t 2 t t a i to h ca d fl av i mtqtairoi ic o rt e aniumetrach z da Y ..m t i tit nin 'i the olub fionl at .1: .,--it .i is rdina y und s a t. pref d to maintain a small amount of titanium trichlorideln the salt mi t grei th c mbenir et add sht y l ss h faradaysfon h solubilization 'ca'thodeper ino'i f titanium tetrachloride iritro lmdln actual pi'a ice, however, small losses of current eificiency generally result in the retention ofa small amount of titanium trichloride in the 'iiielt e ei wnea xa' uy; farada'ys are added through the solubiliz'ation cathode for each mol of titanium tetrachloride introduced. In some cases, depending upon the manner in which the cell is operated, minor proportions of the titanium tetrachloride introduced may be reduced to metallic titanium at the solubilization cathode, or else small amounts of titanium trichloride or dichloride may find their way into the anode compartment. Infiltration of traces of air may cause some of the reduced titanium values in the cell to be partially reoxidized. And finally, a small portion of the salt melt containing some titanium dichloride and trichloride values adheres to the deposition cathode as it is withdrawn from the cell. Any of these eventualities will obviously cause the total amount of current fed through the solubilization cathode to exceed that which would otherwise be expected for a given qantity of titanium produced at the deposition cathode. Reduction of titanium tetrachloride through titanium trichloride and titanium dichloride down to titanium metal may be accomplished in a rapid manner by maintaining the concentrations of titanium dichloride and titanium trichloride within the above-mentioned specified limits.

In order to illustrate more fully the instant invention the following examples are presented:

Example I A mixture of 7300 grams of strontium chloride and 2700 grams of sodium chloride was put into a cell of the general type shown in Fig. 1, except that porous diaphragm surrounded introduction cathode 16 instead of deposition cathode 17. The mixture was heated externally by gas flame to 750 C. Titanium tetrachloride was introduced at the rate of 177 grams per hour into the cell through a tube which terminates in the cell at a point tiibuting the total or t fara'days' p'er molof titaniiim ttr asalts w re acued out bf t 1.0. Current was then assed through the depds ion cathode for 12 hours at anavra'g rate or 45 a j a ing which time titanium chloride addition current supply through solubiliz'ation cathode were continued at the same rate as before. ,The circuits both cathodes were completed through the c I V 1 e A total of 2 ,124 grams of titanium tetrachloride were added at a rate or 177 grains per 1 2 hour period. The system was under argon an esphr'eby adding a stream of argon Eve; the electrolyte in the solubilizatiofi cathode chamber: p

ec e s vicl m t afi ei t r ite i 12 a s e v h a siafi of 5 9 stem f qhlb was collected and condensed: Titanium metal de pbsitedfin' the deposition cathode, iii the forntof poars'e adherent crystals. 'Ihe depps'iting eathode was removed r di bat at i f t l 9 j a i ip ac' i l y a e h c m at e e are th an wa 'd v d en m s e e 6f .ateqfi fln m ead rris 1 r pa r h. 4 one hv 'c ldrt an T em e im dea e scr 'c p flt il w w her. red t s -i. -4 5 m gas i we e over a period of 12 hours cq sp on g tosaj yreldof about 80 '7; of the theoretical qiiantity based ori the amount of titanium tetrachloride added durin g the 12 hour period. At the endof are 12 hour pt 'ou h'e concentration or titanium dichloride and titanium trichloride in both catnode chambers; were substantially the-same as at the start of the 12 hours. These titanium values were allowed to remain in the bell and were eventually deposited in subsequent operation.

, Themolality of the titanium dichloride adjacent to'.the deposition cathode was held between 0.5 and 1.5, while the molality of the titanium trichloride was held between 0.1 and 0.3 during the entire run. The molality of titanium dichloride adjacent to the solubilization cathode was held from 5.0 to 10.0 while the molality of the titanium trichloride adjacent to the solubilization cathode was held form 1.0 to 2.0. The current density on the solubilization cathode was 0.5 ampere per cm The titanium metal recovered was coarse-grained and substantially pure. After melting down to form an ingot it possessed a Brinell hardness of 180. This product possessed suificient purity and ductility for commercial fabrication into rods, sheets and other fabricated products.

Example II A mixture of 730 kg. of strontium chloride and 270 kg. of sodium chloride was put into a cell of the type shown in Figure 3 and the mixture was heated to 750 C. by an alternating current voltage applied across auxiliary heating electrodes (not shown in the figure). Titanium tetrachloride was then introduced at the rate of 0.4 kg. per hour into the cell through tubes terminating near the solubilization cathode. While the titanium tetrachloride was being added, current was supplied to the solubilization cathode at the rate of amperes until the concentration of the titanium dichloride in the electrolyte was 0.32 molal, at which time the concentration of titanium trichloride was found to be 0.24 molal. Current was then supplied through the deposition cathode at an average rate of 176 amperes and was continued for 24 hours. During the 24 hour period 9.6 kg. of titanium tetrachloride were added near the solubilization cathode at the same rate as before, viz. 0.4kg. per hour, and current was supplied through the solubilization cathode continuously at a rate of 114 amperes; This corresponds to acurrent density of 0.15

ampere per cm. at the solubilization cathode, and 0.55 ampere per cm. at the deposition cathode. Both circuits were completed through the common central anode.

Throughout the addition period electrolyte was pumped from the solubilization cathode chamber to the deposition cathode chamber at a rate of 100 kg. per minute and kg. per hour and was collected. The deposition cathode carrying the titanium metal deposit was removed from the bath at 1 hr. intervals and replaced. The deposit was cooled in an inert atmosphere, leached, scraped ed the cathode, water washed and weighed as in Example I.

Over the 24 hour period of operation, 1.9 kg. of titanium metal were recovered, corresponding to about 80% of the theoretical yield based on the amount of titanium tetrachloride added during that period. The concentration of titanium values in the salt melt was substantially the same as at the start of the 24 hour period, and the dissolved titanium values were subsequently deposited in another cycle. The metal produced was substantially pure and sufficiently ductile for commercial fabrication.

As has been shown by the foregoing description and examples the present invention provides a method whereby titanium metal of high purity and ductility may be produced electrolytically. Moreover, it provides an economical method for producing titanium metal directly from titanium tetrachloride. Furthermore, it provides a method whereby titanium metal can be produced continuously on a commercial scale.

While this invention has been described and illustrated by the examples shown, it is not intended to be strictly limited thereto and other modifications and variations may be employed within the scope of the following claims.

We claim:

1. A method for electrolytically producing titanium metal in an electrolytic cell having a fused salt electrolyte selected from the group consisting of alkali metal halides, alkaline earth metal halides, magnesium halides and mixtures thereof, a non-consumable anode, a solubilization cathode and a deposition cathode, andv separating means for separating a product released at the anode from contact with said cathodes, comprising: introducing titanium tetrachloride into said electrolyte in proximity to said solubilization cathode, meanwhile passing electric current between each of said cathodes and said anode, the amount of current added through each cathode being from 1 to 2 faradays at the solubilization cathode and from 2 to 3 faradays at the deposition cathode for each mole of titanium tetrachloride introduced, to produce titanium dichloride and titanium trichloride in proximity to'the solubilization cathode, transferring the so-formed titanium dichloride and titanium trichloride to said deposition cathode and depositing titanium metal on said deposition cathode while releasing chlorine at said anode, and maintaining the molality of the titanium trichloride'no greater than 2.0 and the molality of titanium dichloride no less than 0.05 in proximity to the deposition cathode.

2. Method according to claim 1 in which the molality of titanium trichloride is no greater'than 0.25 times the molality of titanium dichloride and the molality of titanium dichloride, is no less than 0.1 in proximity to the deposition cathode.

3. Method according to claim 1 in which the molality of the titanium values is no less than 0.1 in proximity to the solubilization cathode and the current density in amperes per square centimeter on said solubilization cathode is no more than the numerical molality of the titanium trichloride. e

4. Method according to claim 3 in which the current density of the solubilization cathode is no greater than 2 amperes per square centimeter. a

Great Britain Apr. 5, 1950 Germany July 16, 1935

Claims

1. A METHOD FOR ELECTROLYTICALLY PRODUCING TITANIUM METAL IN AN ELECTROLYTIC CELL HAVING A FUSED SALT ELECTROLYTE SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HALIDES, ALKALINE EARTH METAL HALIDES, MAGNESIUM HALIDES AND MIXTURES THEREOF, A NON-CONSUMABLE ANODE, A SOLUBILIZATION CATHODE AND A DEPOSITION CATHODE, AND SEPARATING MEANS FOR SEPARATING A PRODUCT RELEASED AT THE ANODE FROM CONTACT WITH SAID CATHODES, COMPRISING: INTRODUCING TITANIUM TETRACHLORIDE INTO SAID ELECTROLYTE IN PROXIMITY TO SAID SOLUBILIZATION CATHODE, MEANWHILE PASSING ELECTRIC CURRENT BETWEEN EACH OF SAID CATHODES AND SAID ANODE, THE AMOUNT OF CURRENT ADDED THROUGH EACH CATHODE BEING FROM 1 TO 2 FARADAYS AT THE SOLUBILIZATION CATHODE AND FROM 2 TO 3 FARADAYS AT THE DEPOSITION CATHODE FOR EACH MOLE OF TITANIUM TETRACHLORIDE INTRODUCED, TO PRODUCE TITANIUM DICHLORIDE AND TITANIUM TRICHLORIDE IN PROXIMITY TO THE SOLUBILIZATION CATHODE, TRANSFERRING THE SO-FORMED TITANIUM DICHLORIDE AND TITANIUM TRICHLORIDE TO SAID DEPOSITION CATHODE AND DEPOSITING TITANIUM METAL ON SAID DEPOSITION CATHODE WHILE RELEASING CHLORINE AT SAID ANODE, AND MAINTAINING THE MOLALITY OF THE TITANIUM TRICHLORIDE NO GREATER THAN 2.0 AND MOLALITY OF TITANIUM DICHLORIDE NO LESS THAN 0.05 IN PROXIMITY TO THE DEPOSITION CATHODE.