US2943033A - Preparation of lower titanium halides in a molten salt bath - Google Patents

Description

June 28, 1960 R. D. BLUE ETA!- 2,943,033

PREPARATION OF LOWER TITANIUM HALIDES IN A MOLTEN SALT BATH Filed May 15, 195'? IN V EN TORS. Robe/'2 0. Blue Marsha/l P. Ale/perv HTTOR/VEVS United States Patent PREPARATION OF LOWER TITANIUM HALIDES IN A MOLTEN SALT BATH Robert D. Blue and Marshall P. Neipert, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed May 15, 1957, Ser. No. 659,253

' 5 Claims. (01. 204-64) tion of titanium metal since lower-valence titanium halides thus dissolved may be electrolyzed in an eflicient and practical manner to produce metallic titanium and the by-product halogen, whereas the tetravalent titanium halide cannot be so electrolyzed. Tetravalent titanium halides, e.g., TiCl cannot be electrolyzed to produce titanium because they do not ionizesulficiently to conduct electricity and they cannot be dissolved in molten alkali or alkaline earth halide baths because they are insoluble therein. Furthermore the principal ones which might be so used, e.g., TiCl, and TiBr are unsatisfactory because they volatilize at temperatures too low to remain in the molten salt bath.

The known lower-valence halides of titanium and particularly the chlorides conduct electricity, are soluble in alkali and alkaline earth molten salt baths, and do not volatilize at operation temperatures. Therefore, lowervalent titanium halides dissolved in suitable molten salt baths may be electrolyzed to produce substantially pure titanium.

Titanium is commonly produced by first reducing its ores e.g., brookite or rutile, as by roasting it with calcium or carbon. The titanium thus produced is in a relatively impure state, unsatisfactory for metallurgical uses generally. It is commonly then converted to a halide, particularly to the chloride, by chlorination, as by treating with chlorine gas at an elevated temperature. Since titanium is 'tetravalent except when limiting'conditions exist, e.g., insuflicient chlorine or insuflicient time of contact during the chlorination process, the tetrahalide is produced by such reaction. Attempts to control the reaction of titanium sponge or carbon-contaminated titanium with a halide to produce lower-valence titanium halides have not resulted in a satisfactory product.

The titanium component of the titanium tetrahalide, e.g., tetrachloride, thus produced is thereafter usually reduced to unrefined metallic titanium by reacting the tetrahalide with a metal more electropositive than the titanium in the electromotive series of elements. Magnesium is commonly employed although a number of other metals, e.g., sodium, calcium, or lithium, may be also employed. The titanium thus obtained is in the form of a sponge-like mass'which must be especially treated to convert it to a non-porous compact metal sub stantially free of impurities.

Although a trihalide of titanium, e.g., TiCl can be 2,943,033 Patented June. 28, 1960 gen gas through a red hot tube, such a method is not of economic importance. Attempts to produce lower-valence titanium chlorides by passing TiCl vapor into a reactor at an elevated temperature containing titanium sponge (which had been produced by the reaction of boiling TiCl, with molten magnesium metal in an atmosphere of helium or argon) have not been successful because the lower-valence titanium halides form a coating about the particles of titanium and thereby so retard further reaction of the titanium tetrahalides with the interior of the titanium particle's, even in the presence of a large excess TiCl that the method is rendered commercially unfeasible. I

There is, therefore, a need for an improved method of producing lower halides of titanium, e.g., TiCl and TiCl in a conducting salt bath, from impure sources of titanium including carbides of titanium, from which ductile titanium metal may be recovered by electrolysis of the lower halides.

Accordingly it is an object of the invention to provide a novel method of producing lower-titanium halides dissolved in a salt of a halide or halides of a metal more electropositive than titanium. i

It is a further object to provide a method of converting impure titanium into a form from which substan. tially pure titanium can be subsequently recovered as a ductile non-porous massive metal by electrolysis.

It is a still further object to provide a method of producing lower-valence titanium halides by reacting a halogen-containing reactant with impure titanium including titanium which contains combined carbon.

The method by which these and other objects are obtained will be made clear in the following description and drawing.

The drawing is an elevational view largely in section of an apparatus useful in practicing the invention wherein a halogen-containing substance in vapor form, e.g., TiCl, or TiBr is passed through a molten salt bath containing impure titanium metal.

The invention is based on the discovery that unrefined forms of titanium consisting of at least titanium, including titanium sponge such as that produced by reducing titanium tetrachloride with magnesium, and titanium obtained by reducing the oxidic forms with carbon, e.g., titanium-carbon alloys or titanium carbides, in molten salt baths, are reactable with a halogen-containing compound, e.g., HCl, TiCl or Br in vapor'form passed therethrough, to yield lower-valence titanium halides which dissolve in the salt bath as they form. As a result, a sufficiently high concentration of dissolved lower-valence titanium halides are obtained in the molten salt bath, which are capable'of yielding, on suitable electrolysis, ductile compact cathode deposits of metallic titanium, leaving the impurities in the salt bath.

The invention then consists of the improved method The salt bath selected should be capable of dissolving the lower titanium halide produced; be substantially free from contamination by oxygen, nitrogen, or other elements which would have a detrimental efiect on the prod not; be a conductor of electric current; have a comparatively low meltingpoint; require a higher decomposition potential than the titanium halide produced; be thermally stable at the melting point; and preferably be substantially non-hygroscopic. Halides of alkali and alkaline earth metals and mixtures thereof may be employed. The alkali halides generally predominate in the bath since some alkaline earthhalides are hygroscopic. Salt baths Comprising NaCl, K Cl, LiCl, and MgCl and mixtures of any of these salts are usually employed. Particularly satisfactory are the salt baths of NaCl, KCl, or'miXtures of NaCl-KCl and mixtures of LiClMgCl C'aCl approaching the percentage composition of the eutectic mixtures.

Referring to the drawing in some detail there is shown an apparatus suitable for practicing the invention and particularly adapted to the use of TiCl or TiBr as the halogen-containing source. In refractory furnace setting 10, having gas burner 11 and flue 12in the wall thereof, is positioned graphite-lined steel pot 14 having removable cover 15 thereon. In the bottom portion of pot 14 is transverse plate 16 creating chamber 17 therebelow. In plate 16 are holes over which there are baffles 18.

Passing through openings provided therefor in cover 15 are: feed tube 19 for particulated solid unrefined titanium metal, vaporous halogen or halide inlet tube 20 which extends to and opens into chamber 17, vaporous halide or halogen outlet 21, and outlet 22 for molten bath containing reaction product. Inert gas line 23 opens into line 20. Valve 25 in tube 19, valve 26 in tube 20, valve 27 in tube 21 and valve 28 in tube 22 provide a means for controlling flow therethrough. Gas line 24, opening into tube 19, provides a gas, preferably an inert gas, under pressure for forcing thefiuid contents out of pot 14 through line 22 when desired. Valves 29 and 30 in gas lines 23; and. 24, respectively, are provided for closing off the respective lines as desired in the operation of the apparatus, as explained more fully hereinafter.

Reservoir 31 positioned at the top of tube 19 provides a supply of unrefined titanium particles. Condenser 32 condenses the unreacted vaporous halide leaving pot 14 through tube 21. Line 33 leads to tank 3 4 where the thus-condensed halide is collected to provide a steady source of such halide. through line 35: to proportioning pump 36, driven by motor 37. Vent 38in tank 34 provides an outlet for used inert gas, from the system. Line 39 leads the thus-condensed liquid halide to vaporizer 40. Additional. titanium tetrahalide is fed into vaporizer 40 from supply tank 41 through tube 42. The rate of feed through tube 42 is, controlled by valve 43. Gas burner 44 provides heat for vaporizing the halide in vaporizer 40. The thus-vaporized halide passes out of vaporizer 40 into vaporous halide feed-line 20.

In carrying out the invention, using the apparatus shownin the drawing, an alkali or alkaline earth metal halide or a mixture thereof is placed in graphite-lined steel pot 14 and heated by means of burner 11 to a temperature sufficiently high to melt the salt to form bath 45. Titanium sponge, titanium-carbon alloys, or other unrefined titanium in the form of pieces 46 is. placed in the bath as by feedingthrough tube 19 from reservoir 31 by opening valve 25.

Burner 44 is lighted and a titanium tetrahalide, e.g., liquid TiCli 47 (or particulated TiBr is placed in reservoir 41 and fed into vaporizer 40 through line 42 by opening valve 43 therein. In vaporizer 40 it is. converted to a vapor by the heat from burner 44. An amount of the tetrahalide is fed into vaporizer 46 to maintain a sufficient supply of boiling titanium tetrahalide therein at a level below the openings leading therefrom to continuously provide a source of vaporous titanium tetrahalide. By opening valve 26 in tube 20, the vaporous titanium tetrahalide from vaporizer 40 passes through tube 20 down into chamber 17 in the lower part of pot 14. Valve 27 in line 21 is also opened to provide complete circulation through reactor pot 14.

When using TiBr or TiCl it is preferable to introduce inert gas under pressure through line 23 by opening valve 29. By passing the inert gas, e.g., helium, through a common line with the vaporous halide-bearing material, the inert gas is saturated with the tetrahalide vapor before it enters the reactor. The inert gas thus introduced creates greater pressure to force the tetrahalide vapor through the bath and aids in the agitation of the bath while the tetrahalide vapor is rising therethrough. After the titanium tetrahalide vapor enters chamber 17, it passes upwardly through the openings in plate 16 where it is broken into small bubbles and dispersed by baffies 18, and thereafter rises through bath 45 containing particulate impure titanium 46. Lower-valence titanium halides, e.g., TiCl and TiCl are formed by the ensuing reaction and are dissolved by the bath. Unreacted titanium tetrahalide passes off through tube 21, is condensed in condenser 32 (the temperature therein not being sufiiciently low to cause solidification if TiBr is used). The liquid titanium tetrahalide from condenser 32 drops through line 33 into tank 34 from which it is pumped by pump 36 out through tube 35 and up tube 39 into vaporizer 40. Spent inert gas is vented through vent 33 in tank 34.

After the concentration of the lower valence halides has approached the saturation point in the bath, valves 25, 26, 27 and 29 are closed and the bath, thus enriched with the lower-valence halides, is removed by opening valve 30 in gas line 24 and valve 28 and tube 22 and introducing compressed inert gas, e.g., argon, through line 24 which forces the liquid bath and lower-valence halides dissolved therein out through tube 22 into a receiver (not shown).

As an alternative mode of practicing the invention, an apparatus may be used in which the impure titanium is placed in a porous or perforate basket of a conductive material, e.g., of graphite, and placed in a heated reaction vessel, e.g., melting pot 14 containing the molten halide salt bath of the invention.

When a halogen-containing substance is employed which exists as a vapor at room temperatures, e.g., Br C1 or HCl, the vaporizer and condenser assembly of the apparatus shown in the drawing may be eliminated and a halogen source such as a steel tank of the halogenbearing vapor or a. generator of such halogen-bearing substance be'substituted for such assembly by connecting the outlet of the tank or generator to tube 20 and by compressing or by collecting the excess halogen or halide by known meansv as it leaves the reaction vessel.

. As an alternative mode of removing the bath enriched with the lower-valence halides, a less efiicient but simpler procedure is to employ an apparatus which is. not equipped with tubes 22 and 24 shown in Fig. 1. In such alternative mode, after stopping the reaction substantially as above, cover 15 is removed and the enriched molten bath pumped, dipped, or siphoned from the pot into a place of storage or directly into an electrolytic cell for electrolysis of the, lower-valance titanium halides therein.

As, a further embodiment of the invention, the pot containing the molten salt bath and particulate titaniumbearing material may be itself an electrolytic cell wherein lower-valence titanium halides formed by the introduetion of a halogen source into the cell according to the invention may be electrolyzed and titaniummetal recovered from the cathode and the halogen at the anode without transferring the thus enriched bath from the reaction pot prior to the electrolysis.

In the electrolysis of lower-valence titanium halides thus dissolved in a salt bath, whether electrolysis is carried on in a cell which is separate from the reaction pot or is carried on in the reaction pot, titanium ions move toward the cathode and the halide, e.g., the bromide or chloride ions move toward the anode. The titanium collects at the cathode as substantially pure titanium metal. If the electrolyte pot is made the anode so that the titanium particles thereby form part of the anode, or if the anode consists of a titanium bar or rod to be consumed, the bromine or chlorine liberated then reacts alkaline halide salts varies.

with the titanium particles in the bath or with the titanium bar anode to form additional lower-valence titanium halides so that little or no bromine or chlorine gas leaves the bath at the anode.

Representative reactions which yield lower-valence titanium halides Within a molten salt bath according to the invention are represented by the following equations in Table I below:

Table I Titanium sponge or titanium alloys containing up to 4% carbon present in the reactions represented by the above equations, or some other impure titanium metal present reacts with some of the TiCl thus formed to produce TiCl Ti+2TiCl TiCl The invention is not limited to reactions involving titanium alloys containing not over 4% of the carbon component but the presence of TiC, where the carbon component is in excess of 4%, slows the reaction. and

also results in little reduction of trichloride to the dichloride.

The concentration of Ti and Ti++ in alkali or For example Ti+++, formed upon reacting Ti metal (alloyed with 4% carbon) with HCl gas, reaches a concentration of 10% at 900 C. in about six hours in a molten KClNaCl eutectic bath. Ti+++ formed by reacting titanium sponge with HCl gas reaches a concentration of about 6.25% in about 2 hours at 750 C. in the molten KCl-NaCl eutectic bath. Ti++ concentration is affected by the presence of Ti+++ ions. For example, the Ti++ concentration reaches 2% in the molten KCl--NaCl eutectic when the Ti concentration is 2.5% but the concentration of the Ti++ drops 01f to about 1.25% when the Ti concentration is about 5% and drops below 0.1% when the Ti+++ concentration builds up to about 10%. In order that an appreciable percentage concentration of the divalent titanium ion be reached, it is advisable to provide an excess of unrefined titanium in the bath and limit the quantity of the tetrahalide feed so that sufficient titanium is present to react with the TiCl formed before the percentage of Ti+++ has exceeded about 2% which, in terms of TiCl is about 6.4%. V

Table II which follows sets forth the determined concentrations Ti++ and Ti+++ as mixed TiCl and TiCl in specified alkali and alkaline earth chloride baths at 900 C.

The rates of reaction of the various reactants contemplated by the invention vary with the reactants used.

Other conditions, such as state of subdivision and surface condition of the impure titanium also affect the rate of reaction but to a relatively less extent than dothe reactants themselves.

Table III-below shows the relative reaction rates neces sary to form 1 gram-atom of Ti+++ for certain reactions when the rate of reaction of titanium sponge andHCl is arbitrarily taken as 1.0.

Table III Relative Reaction Reaetants Tempera- Rate To ture 0. Form 1 gm.-'atom oi T+++ 750 1.0 750 0.25 900 0.53 900 0.10 750 0.03 Ti(4% CH-HBr... 750 0. 17 Tl(4% C)+hellum saturated with T1014 at 124 C 760 0.08 'IlC-I-hellum saturated with T1014 at 124 O 820 0.06

The rates of reaction of titanium sponge and HCl vapor according to the invention are further illustrated by the following example:

900 grams of equimolar TNaCl-KCl eutectic salt mixture were melted in a pot to form a bath. Inert gas was supplied in sufficient amount to form a blanket over the bath. The temperature of the bath was maintained at about 750 C.

TiCl which comprises admixing particulate titanium-.

bearing material containing at least 90 percent titanium selected from the class consisting of titanium sponge and titanium-carbon alloys containing not more than 4 percent carbon in a molten salt bath selected'from the class consisting of alkali metal and alkaline, earth metal halides and mixtures thereof, heating said bath to a temperature of between 750 and 900 C. under'a protective atmosphere of an inert gas, and passing a hydrogen halide gas selected from the class consisting of HCl and HBr into said molten salt bath at said temperature to contact the titanium-bearing material therein.

2. The method of "claim 1 wherein the halogen-containingvapor is released under pressure'in the bath near the bottom thereof and caused to bubble up through said bath. 3. The method of claim 1 wherein the salt bath is a mixture of KCl and NaCl.

4. The method of claim 1 wherein the salt bath is NaCl;

5. The method of claim 1 wherein the salt bath is KCl.

ReferencesCited in the file of this patent UNITED STATES PATENTS; I

"/3 grams of M4 inch mesh titanium sponge having a bulk density ofapproximately l were introduced in a graphite, basket immersed in the bath. Dry HCl gas was bubbled through the mixture in excess of the i stoichiometric requirement. TiC-l was formed at a rate a

Claims (1)

1. THE METHOD OF PRODUCING A MIXTURE OF TICL2 AND TICL3 WHICH COMPRISES ADMIXING PARTICULATE TIANIUMBEARING MATERIAL CONTAINING AT LEAST 90 PERCENT TITANIUM SELECTED FROM THE CLASS CONSISTING OF TITANIUM SPONGE AND TITANIUM-CARBON ALLOYS CONTAINING NOT MORE THAN 4 PERCENT CARBON IN A MOLTEN SALT BATH SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL HALIDES AND MIXTURES THEREOF, HEATING SAID BATH TO A TEMPERATURE OF BETWEEN 750* AND 900* C. UNDER A PROTECTIVE ATMOSPHERE OF AN INERT GAS, AND PASSING A HYDROGEN HALIDE GAS SELECTED FROM THE CLASS CONSISTING OF HC1 AND HBR INTO

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