US2731404A - Production of titanium metal - Google Patents

Description

t me v United States Patent PRODUCTIQN OF TITANIUM METAL Eugene Wainer, Cleveland Heights, Ohio, assignor, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey No Drawing. Application October 29, 1952, Serial No. 317,577

13 Claims. (Cl. 2ll4-64) This invention relates to the production of titanium metal and, more particularly, to a novel method of producing the metal by electrolysis.

It has been ascertained heretofore that the titanium metal cathodically deposited by electrolytic decomposition of a fused bath comprising a complex fluoride, such as sodium or potassium fluotitanate, is readily amenable to melting down into ingot form with a minimum of concurrent contamination. This attribute is a result of the relatively coarse particle size of the crystals of titanium so obtained because the coarseness of the metal deposit minifies surface oxidation of the particles during the washing operation required for removal of entrained salt from the deposit. Unfortunately, however, this electrolytic operation is accompanied by a progressive increase in the simple fluoride content of the bath as a lay-product of the decomposition of the complex fluoride. As the simple fluoride content of the bath increases, anode effects within the bath become more pronounced and there is a consequent diminution in the current which can be passed through the cell. The resulting requirement for frequent replacement of the bath renders the method commercially unattractive at the present time.

I have now discovered that the aforementioned advantages may be realized and the disadvantages eliminated by electrolytically decomposing a titanium tetrahalide such as titanium tetrachloride, tetrabromide or tetraiodide in a fused salt bath containing as an essential constituent one or more of the aforementioned complex fluorides. Thus, I have discovered that when electrolyzing conditions are established which will effect electrolytic decomposition of titanium tetrahalide in the bath without decomposition of the complex fluoride component of the bath, the cathodically deposited titanium metal has the coarseness characteristic of that produced by actual decomposition of the complex fluoride but the bath does not appreciably change in its composition throughout long periods of sustained operation. Accordingly, the method of my present invention is one in Which metallic titanium is produced directly from a titanium tetrahalide other than the tetrafluoride. This novel method comprises establishing a molten bath composed essentially of an alkali metal fluotitanate, establishing between electrodes in contact with the bath a voltage below the decomposition voltage of the fiuotitanate but greater than the decomposition voltage of the titanium tetrahalide in the bath, and introducing the titanium tetrahalide into the bath at a rate sufficient to maintain a cathode current density of at least 50 and not more than 500 amperes per square decimeter. Under these conditions, the bath exhibits the capacity to hold the titanium tetrahalide in solution and thus permit its electrolytic decomposition without significant loss of the tetrahalide by volatilization from the bath.

The fused salt bath in which a titanium tetrahalide other than the fluoride is electrolytically decomposed in the practice of my invention contains, as its essential "ice constituent, a complex fluoride such as sodium or potassium fluotitanate (NazTiFs and KaTiFs, respectively). Although the maximum benefit in coarseness of particle size and metal recovery efllciency is attained with a bath 5 composed exclusively of one or more molten alkali metal iiuotitanates, the advantages of the process may be realized when the bath contains as little as about 25% by weight of the alkali metal fluotitanate with the remainder composed of one or more alkali metal halides other than the fluoride. When such a simple alkali metal halide is used as a diluent component of the fluotitanate bath, it is preferable, although not essential, that the halide of the alkali metal be the same as the halide constituent of the titanium tetrahalide introduced into the bath for 1 electrolysis. The advantage in adding such an alkali metal halide to the fiuotitanate bath is that this addition lowers the melting point of the bath and permits the use of a lower operating temperature during electrolysis which, in turn, is accompanied by a greater apparent solubility of the titanium tetrahalide in the bath.

Thus, with baths composed of a single alkali metal fluotitanate, an operating temperature of 800 to 850 C. will be required, Whereas with baths further containing one or more alkali metal halides the operating temperatore may be lowered to about 600 to 650 C.

An essential requirement of the bath is that it be anhydrous. The alkali metal fluotitanates contain water of crystallization all of which can be removed by heating the fluotitanate to a temperature within the range of 15 to 360 C. under a vacuum of about 1 millimeter of mercury or less. The aforementioned diluent components, if used, generally do not require dehydration but it is advisable to add such a diluent salt to the fluotitanate prior to dehydration of the latter so as to insure the completely anhydrous quality of the bath which is subsequently obtained when the mixture of anhydrous components is heated to a fusion temperature. In this way, the titanium metal deposited on the cathode during electrolysis will be completely free of contamination by oxy- 49 gen and there will be virtually no loss of the titanium tetrahalide by hydrolysis.

The titanium tetrahalides which may be used in practicing the method of my invention comprise titanium tetrachloride, titanium tetrabromide and titanium tetraiodide. Each of these compounds is completely vapor ized at temperatures considerably below those at which the aforementioned salt baths melt, and consequently the bath will assimilate the tetrahalide while the latter is in the gaseous state. For this reason, I have found it 50 advisable to deliver the tetrahalide to the bath in the gaseous state by heating the tetrahalide exteriorly of the bath, and l. have found it to be particularly advantageous to dilute this gaseous titanium halide with an inert carrier gas such as pure argon, helium, or the like. in this way the local concentration of the titanium tetrahalide in the bath is maintained at a sufiiciently low level to mit its ready assimilation by the bath under electrolyz conditions.

The electrolyzing conditions required for decomposition oi the titanium tetrahalide in the fiuotitanate bath consist of a decomposition voltage below that at which any significant amount of the fluotitantae is decomposed but sufficient, in cooperation with the rate of supply of the titanium tetrahalide to the bath, to maintain in the bath cathode current density of at least 50 and not more than 500 amperes per square decimeter. The at tainment of this result is facilitated by introducing the titanium tetrahalide into the bath closely adjacent the cell anode, and in furtherance of this aim I have found it to be advantageous to provide an anode area, in the form of either one or a plurality of anodes, which is significantly greater than the cathode area in contact with the bath. The intimate association of the titaniumtetrahalide charge with the anode. is also facilitated by compartmentation of the cell suchas to maintain the titanium tetrahalide in-thevicinityof: the anode while nevertheless permitting, by means of a,multiplicity of small openings in the partition, communication between the bath in the anode and'cathode;compartments. With all of these expedients, I have found that cathode current densities within therange of ,200 -to 45O amperes per square decimeter promote particularly satisfactory operation, high current efliciency, and high,- metal recovery e y.

A variety of cell designs may be used in prac ing the method of my invention. For example, effective results have been obtained with a cell composed of a graphite crucible which served asthe anode and a centrally positioned nickel rod as the. cathode. The titanium tetrahalide was introduced. into the fused salt bath within the crucible by admixing the tetrahalide vapors with dry argon and then chargingthe resulting gaseous mixture to the bath through a hollow graphite tube having its lower end pluggedandits lower side walls perforated with a multiplicity-of fine holes. The best results with this cell design were obtained. when the titanium tetrahalide delivery tubewas positioned close to the side wall of the crucible-anode. Another useful cell construction comprised a graphite crucible which contained the fused salt bath and which was provided with a nickel rod as the cathode and 'a hollow graphite tube such as that referred to hereinbefore but serving in this instance .as an anode. A plurality of these hollow anodes in a single cell gave particularly effective results by olfering a relatively large anode area to the titanium tetrahalide vapors which issued through the small perforations in the lower side walls of the anodes and which rose upwardly in the bath immediately adjacent the anode surf e. A third cell arrangement which-has been used eflectively comprised a graphite crucible whichserved as the anode and a centrally positioned nickel'rod serving as the cathode. A graphite cylinder was lowered into the cell until it nearly touched the bottom of the crucible, and the lower portion of this cylinder was provided with a number of small holes. The titanium tetrahalide was then introduced into the cell by delivering it through a tube extending downwardly close to the bottom of the annular anode compartment'defined by the crucible walls and the cylindrical graphite sleeve. In each of these modifications, the cell was mounted within a gas-tight enclosure so that the ambient atmosphere was excluded and the portion of the nickel cathode positioned above the upper level of the bath was protected with a surrounding graphite sleeve. The elevated bath temperature was maintained by heat exteriorly applied to the closed cell structure.

The method of my invention may be practiced in the manner described hereinbefore with current efficiencies upward of 50% and with metal recovery efficiencies,

based upon the amount of titanium metal deposited by electrodecomposition of the titanium tetrahalide, close to 100%. However, I have found it advantageous to so correlate the electrolyzing conditions and the titanium tetrahalide charge rate as to obtain metal recovery elliciencies of about 9095% in order to insure the delivery of the tetrahalide into the bath at a rate somewhat in excess of that at which it can be decomposed by the prevailing electrolytic conditions and thus preclude electrolytic decomposition of the diluent bath components.

As will be apparent from this control feature, I have found that the titanium tetrahalide can be preferentially electrolyzed in a fluotitanate-containing bath without significant decomposition of the fiuotitanate provided that there is always present in the bath enough of the charged tetrahalide to satisfy the electrolytic potentialities prevailing within the cell.

Thepractice of my invention may be illustrated by the following specific examples:

4 Example I nickel rod was inserted into the center of the bath and that portion of the rod .above the upper level of the bath was encased in a graphite sleeve. Exteriorly of the cell, titanium tetrachloride was heated to a temperature of -120 C. in a closed vessel through which anhydrous argon was bubbled, and the effluent mixture of argon and titanium tetrachloride vapor was introduced through an inert tube into the bath at a position close to the bottom of the crucible and close to its, side wall. The bath temperature was maintained at about 725? C. and the cell'voltage was adjusted to establish and maintain a cathode current density of 400 amperes per square decimeter by introducing the titanium tetrachloriderargon mixture into the bath at a substantially uniform rate for: a period of 1 hour during which 430 grams of the tetrachloride were charged to the cell. A metallic. titanium cathode deposit was obtained which, after being thoroughly washed and vacuum dried, weighed grams. The metal was thus obtained with a metal recovery efiiciency of approximately 55% at a current efficiency between 50 and 55%. The washed and dried particles of titanium metal had a particle size in excess of l50'mesh (Tyler Standard).

Example 11 The operation described in Example I was repeated with identical temperatures and electrical conditions, the only difference being that the cell was provided with a single nickel cathode and four hollow graphite tubes closed at their bottom end but provided along their lower side walls with a multiplicity of small holes. The hollow graphite tubes served both as anodes and as the means for introducing the titanium tetrachloride-argon mixture into the bath. Thisarrangement made possible the introduction of a larger quantity of titanium tetrachloride into the bath than that which was possible with the cell de-- scribed in Example I, and the washed and dried metallic titanium obtained in this four-anode cell represented a metal recovery elficiency of approximately 87% at a current efiiciency of about 77%.

Example 111 The operation described in Example I was repeated under identical physical and electrical conditions except for the use, asthe salt bath, of a mixture composed of 90 parts of potassium fiuotitanate and 10 parts by weight of sodium chloride, the mixture being dehydratedat a temperature of 200 C. under a vacuum of less than l1millimeter of mercury. The metal recovery efiiciency was 70% at a current efficiency of 65 The titanium metal 7 deposited on the cathode was coarser than that deposited For example, the maintenance of a cell atmosphere-pressure of 5 to 20 pounds per-square inch above normal or ambient atmosphericpressure-promotes greater solubility of the titanium-tetrahalide in thebathand'hence; leads to more efficient utilizationandmore efiicient electrolysis" of the tetrahalide. Such a superatmospheric pressure may be provided readily by supplying the inert cell atmosphere gas such as argon or helium under a positive gauge pressure, and of course the titanium tetrahalide vapors simultaneously supplied to the cellwill be delivered under the same pressure.

It will be seen, accordingly, that the method of my present invention makes possible the production of titanium metal directly from a titanium tetrahalide as the source material introduced into a fused salt electrolyzing bath. The metal is thus produced, in the practice of the invention, by electrolytic decomposition of the titanium halide without degenerative decomposition of the fluotitanate. The term degenerative decomposition is used herein and in the claims to define such decomposition of the fluotitanate component of the bath as will cause a progressive change in the composition of the bath and thus lead to the necessity for periodic regeneration or replacement of the bath. However, it appears conceivable on the basis of information presently available that the fluotitanate may undergo some partial change in composition during initial electrolysis but that the resulting form or variation of the fluotitanate is stable'throughout subsequent electrolysis to the extent that it does not significantly alter the bath composition as the electrolysis continues.

I claim:

1. The method of producing metallic titanium from a titanium tetrahalide other than the fluoride which comprises: establishing an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fiuotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, establishing 21 voltage between electrodes in contact with the bath, introducing the titanium tetrahalide into the molten bath, main taining the voltage between the said electrodes sufficient to maintain a cathode current density of at least 50 and not more than 500 amperes per square decimeter during the introduction of the tetrahalide, thereby depositing titanium at the cathode.

2. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fluotitanates and mixtures of at least one alkali metal fiuotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the electrodes in contact with said bath, introducing the titanium tetrahalide into the molten bath, maintaining the voltage between the said electrodes below the voltage at which alkali metal is deposited on the cathode but sufilcient to deposit titanium on the cathode whereby decomposition of the titanium tetrahalide is effected and titanium is deposited on the cathodic electrode.

3. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrailuoricle which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting of at least one alkali metal fluotitanate, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the electrodes in contact with said bath, introducing the titanium tetrahalide into the molten bath, maintaining the voltage between the said electrodes below the voltage at which alkali metal is deposited at the cathode but sufiicient to deposit titanium on the cathode whereby decomposition of the titanium tetrahalide is effected and titanium is deposited on the cathodic electrode.

4. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fiuotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the electrodes in contact with said bath, introducing the titanium tetrahalide into the molten bath closely adjacent to the anodic electrode, maintaining the voltage between the said electrodes and the said bath suflicient to provide a cathode current density of between about and 500 amperes per square decimeter, thereby depositing titanium on the cathodic electrode.

5. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten batth consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fluotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the electrodes in contact with said bath, introducing the titanium tetrahalide into the molten bath closely adjacent an anode surface having a greater area than that of the cathode, maintaining the voltage between the said electrodes suflicient to provide a cathode current density of between about 50 and about 500 amperes per square decimeter, whereby titanium is deposited on the cathodic electrode.

6. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing an electrolytic cell, establishing therein an anhydrousmolten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fiuotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducing a gaseous mixture of the titanium tetrahalide vapor and an inert gas into the molten bath, maintaining the voltage between the said electrodes below the voltage at which alkali metal is deposited on the cathode but sutficient to deposit titanium on the cathode whereby decomposition of the titanium tetrahalide is eifected and titanium is deposited on the cathodic electrode.

7. The method of producing metallic titanium from titanium tetrachloride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fluotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducing titanium tetrachloride into the molten bath, maintaining the voltage between the said electrodes below the voltage at which alkali metal is deposited on the cathode but sutlicient to deposit titanium on the cathode whereby decomposition of the titanium tetrachloride is effected and titanium is deposited on the cathodic electrode.

8. The method of producing metallic titanium from titanium tetrachloride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting of at least one alkali metal fluotitanate, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducing titanium tetrachloride into said molten bath, maintaining the voltage between the said electrodes sufficient to provide a cathode current density of between about 50 and about 500 amperes per square decimeter, whereby titanium is deposited on the cathodic electrode.

9. The method of producing metallic titanium from titanium tetrachloride which comprises: providing an electrolytic cell, establishing therein ananhydrous molten bath consisting ofv an alkali metal fluotitanate, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducing titanium tetrachloride into the molten bath closely'adjacent to the anodic electrode, maintaining the voltage between the said electrodes sufiicient to provide a cathode current density between about 5.0 and about 500 amperes per square decimeter, whereby titanium is depositedon the cathodic electrode.

10. The method of producing metallic titanium from titanium tetrachloride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt'from the. group consisting of alkali metal fiuotitanates and *mixtures of'at least one alkali-metal fluotitanate with at least one alkali metal halide. other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducing a gaseous mixture of titanium tetrachloride; vapor; and an inert gas into the molten bath, maintainingthe voltage between the said'electrodes suflicient to provide a cathode. current density of between about 50 and 500 amperesper square decimeter, whereby titanium is deposited on the cathodic electrode.

11. The method of producing metallic titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing. an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fiuotitanates and mixtures of atleast one alkali metal fiuotitanate' with at least one which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group alkali metal halide other than the fluoride, maintaining consisting of alkali metal fiuotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other. than the .fluoride, maintaining above the bath; an' inert cell atmosphere at a pressure of 5 to 20 pounds per square inch above ambient atmospheric pressure, providing electrodes in. contact with said anhydrous molten bath, establishing a voltage between the said electrodes, introducingthe titanium tetrahalide into the molten bath, maintaining the voltage between the said electrodes 'below the voltage at which alkali metal is deposited at the cathode but suflicient to deposit titanium on the cathode whereby decomposition of the titanium tetrahalide is effected and titanium is deposited on the cathodic electrode.

13. The method of producing metallic. titanium from a titanium tetrahalide other than titanium tetrafluoride which comprises: providing an electrolytic cell, establishing therein an anhydrous molten bath consisting essentially of at least one alkali metal salt from the group consisting of alkali metal fiuotitanates and mixtures of at least one alkali metal fluotitanate with at least one alkali metal halide other than the fluoride, providing electrodes in contact with said anhydrous molten bath, establishing a voltage between said electrodes, introducing the titanium tetrahalide into the bath at a rate in excess of the rate at Which the tetrahalide is electrolytically decomposed'in the bath, maintaining the voltage between the said electrode below the voltage at which alkali metal deposits at the cathode but suificient to deposit. titanium on the cathode whereby decomposition of the titanium tetrahalide is eifected and titanium is deposited on the cathodic electrode.

7 References Cited in the file of this patent UNITED STATES PATENTS Japan Sept. 26, 1952

Claims (1)

1. THE METHOD OF PRODUCING METALLIC TITANIUM FROM A TITANIUM TETRAHALIDE OTHER THAN THE FLUORIDE WHICH COMPRISES: ESTABLISHING AN ANHYDROUS MOTEN BATH CONSISTING ESSENTIALLY OF AT LEAST ONE ALKALI METAL SALT FROM THE GROUP CONSISTING OF ALKALI METAL FLUOTITANATES AND MIXTURES OF AT LEAST ONE ALKALI METAL FLUOTITANATE WITH AT LEAST ONE ALKALI METAL HALIDE OTHER THAN THE FLUORIDE, ESTABLISHING A VOLTAGE BETWEEN ELECTRODES IN CONTACT WITH THE BATH, INTRODUCING THE TITANIUM TETRAHALIDE INTO THE MOLTEN BATH, MAINTAINING THE VOLTAGE BETWEEN THE SAID ELECTRODES SUFFICIENT NOT MORE THAN 500 AMPERES PER SQUARE DECIMETER DURING THE INTRODUCTION OF THE TETRAHALIDE, THEREBY DEPOSITING TITANIUM AT THE CATHODE.