US2787539A - Production of refractory metals - Google Patents

Description

April 1957 A. R. CONVKLIN 7 2,787,539

I PRODUCTION OF REFRACTORY METALS Filed Oct. 30, 1952 INVENTQR ALFRED 'R. CONKLIN Alma-4g ATTORNEY United States Patent 1 2,787,539 PRODUCTION OF REFRACTORY METALS Alfred R. Conklin, Wilmington, Del., asslgnor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application October 30, 1952, Serial No. 317,787 7 Claims. (Cl. 75-845) This invention relates to the preparation of refractory metals, such as titanium and zirconium, and more particularly to the preparation of such metals by reduction of their volatile halides with an active reducing metal. More specifically, it pertains to titanium metal production in a batch type of operation wherein titanium tetrachloride is reduced in a closed reactor at an elevated temperature with a reducing metal such as magnesium.

The production of titanium metal has recently become of considerable commercial importance. One type of batch process for effecting its production comprises that disclosed in U. S. Patent 2,205,854. In that process a reaction vessel containing a charge of magnesium metal is heated under an inert atmosphere to induce melting of the metal. Titanium tetrachloride is then admitted to the vessel wherein it vaporizes and reacts with the molten magnesium to form titanium metal sponge in accordance with the equation:

The temperature of reaction is usually maintained between the melting point of the magnesium chloride byproduct and the boiling point of magnesium, with temperatures of the order of 950-1050" C. usually prevailing. If the reaction goes to theoretical completion, only 11% of the intermingled end products (MgClz and Ti) volume is occupied by titanium, the remainder being filled by the salt. Usually the reaction is run to about 78% use of the Mg, 2. practice which prevents excessive formation of the lower titanium chlorides.

It has been customary in an improvement upon the foregoing operation to drain out as much of the byproduct salt as possible from the reactor while said salt is still in the molten state. When this draining step is effected, it is very desirable that draining of any of the liquid reducing metal, i. e., magnesium, be avoided. To prevent this, the draining step is resorted to only after about 60% of the reaction has been completed, i. e., after 60% of the final amount of the TiCl4 has been added. This has been considered to be a critical point at which there is enough titanium sponge formed to retain the re maining magnesium by adhesion to thus permit the uncontrolled bottom discharge of a major portion of the molten salt. After the draining (which is done under an inert atmosphere of argon or helium in the reaction chamber) TiCli addition is again efiected for reaction with the uncovered magnesium in the sponge. By recourse to tapping out the salt after 60% completion of the reaction, a slightly denser sponge is obtained, being about 14.5% of the ultimate density of the metal, instead of 11% when draining is not practiced.

The sponge metal obtained after the final draining is usually further separated from the salt and residual magnesium by vacuum distillation and/or aqueous leaching treatment. It is quite porous and, due to the relatively great area of certain portions thereof, is likely to be pyrophoric in character. On grinding or milling it produces undesirable fines which are not only hazardous but react with oxygen and nitrogen on exposure to air and during leaching to disadvantageously decrease the purity and ductility of the final metal product.

It has now been found that prior processes for titanium and other refractory metals of the type referred to can be advantageously improved whereby a better operation Patented Apr. 2, 1957 with production of a superior type of metal product can be readily achieved. Accordingly, it is among the objects of this invention to overcome the above and other disadvantages in prior methods for producing said metals and to provide novel and effective procedures for accomplishing such objects. A particular object is to provide a novel process for obtaining a denser sponge product through the expediency of a more efiicient type of process. A further object is to obtain a greatly increased apparatus capacity and production of a purer form of sponge metal and final metal product. Other objects and advantages of the invention will be apparent from the ensuing description and accompanying diagrammatic drawing showing a vertical, sectional view of one form of apparatus in which the invention can be carried out.

These and other objectives and advantages are attained in this invention which comprises reducing a volatile metal halide, particularly of titanium or zirconium, with an active molten reducing metal within a closed reactor and withdrawing molten by-product metal halide from the reactor prior to 60% completion of the reduction reaction.

In a more specific and preferred embodiment, the invention comprises reducing a metal chloride, such as TiCii, at an elevated temperature with a molten reducing metal, such as Mg, within a closed reactor, and commencing the withdrawal of by-product molten metal chloride from said reactor when completion of from about 15% to 50% of the reduction reaction has taken place.

Referring to the accompanying drawing, there is shown a reaction vessel 1 composed of corrosion-resistant steel or other desired, useful type of metal or alloy, having a close-fitting cover or header 2 adapted to be bolted or otherwise secured in air-tight relationship to the vessel 1 and with a water-cooled gasket 3 suitably interposed therebetween. A flue outlet 4 provided with a suitable closure member 5 is situated in said cover element, whereby during a subsequent vacuum distillation operation volatile residues can be removed from sponge metal reaction product formed in the reactor. An inert gas (argon, helium, etc.) inlet 6 is associated with the flue 4 whereby an inert atmosphere of such gas (should it be desired) can be maintained on the reactants and reaction products during and subsequent to the reduction reaction. A valved inlet 7 is also provided in said header through which regulated amounts of TiCl4 or other metal halide reactant can be charged to the system. A conduit 8 containing an associated pressure gauge 9 and a relief valve 10 is also carried by the cover 2, and is maintained, as shown, in open communication with the interior of the reactor 1. A sheet steel or other suitable form of protective liner 11 shaped to conform to the inner contour of the reaction vessel 1 is disposed within said vessel while a perforated or other form of suitably apertured supporting plate member 12 is provided in the lower part of the liner and vessel. ciated valve control mechanism 14 is also provided in the bottom of the vessel 1, with the outlet forming, as shown, a continuation of liner 11. The reactor and its contained liner and supporting element is disposed within a suitably insulated furnacing element 15 provided with electrical or other desired types of heating elements 16.

In practically adapting the invention in an apparatus of the type just described, to reduce, for example, TiCl4 with Mg, the latter reactant is charged in solid state into the reactor which is then sealed from the atmosphere and argon charged therein to purge contaminants therefrom and provide an inert atmosphere therein. The heating elements are then activated until melting of the magnesium occurs. Thereupon, the TiCli reactant is admitted at a controlled rate to initiate the reduction reaction which takes place at temperatures ranging upward from about An outlet 13 containing an asso- 750 C. During the earlier stages of this reaction and after it has progressed only to the point where between and preferably between and 50%, of the TiCl4 being charged to the system has been consumed, the molten by-prodnct MgClz is valved off from the bottom of the reactor through outlet 1-3 and valve control means 14. Such MgCiz withdrawal is continued through the subsequent stages of the reduction, the withdrawal rate being preferably regulated to correspond to the make rate, e; g., is substantiallythe same as the feed rate of TiCl4 in pounds. Upon completing the addition of the total amount of TiCh to be charged, further reaction is discontinued and the sponge metal reaction product is subjected to conventional purification treatment. Thus, while it still remains within the reactor, it can be subjected to vacuum distillation treatment and recovery effected of the denser form of titanium metal sponge Which the invention inherently affords.

To a clearer understanding of the invention, the ensuing specific examples are given. These are illustrative only and are not to be construed as in limitation of the invention:

Example I Employing an apparatus of the type shown in the drawings, consisting of a cylindrical iron retort 10" in diameter, three feet in height, and fitted with a bottom outlet and a steel gate valve, fifteen pounds of solid, clean magnesium metal was placed on the supporting plate within the retort. The head element was then bolted in place and the assembly placed in a furnace. After purging with argon, heating to 825 C. was effected to melt the magnesium. Titanium tetrachloride was then admitted at a rate of abou 15 lbs./hr., the ensuing reaction being controlled by means of regulating the argon flow and reducing the temperature of the furnace by circulation of air around the retort when necessary to keep the retort walls below about 950 C. When 12 lbs. of TiCl4 had been added, nine pounds of MgCl2 were drained out of the reactor through the valved bottom outlet. Nine additional pounds of MgCl2 were thereafter removed for each twel e pounds of TiCl4 added and until a total of forty-eight pounds of TiCLi had been introduced and thirty-six pounds of MgClz had been withdrawn. Removal of the remaining MgClz and unreacted Mg which could not be drained out was effected by subjecting the reaction product to vacuum distillation Within the retort. The recovered ductile titanium sponge was found to have an apparent density of 80#/ cu. ft. as compared with 48#/cu. ft. for a product obtained by draining the MgClz only after 60% of the TiCli had been added. The sponge was equal in purity to the product obtained from the prior art procedure and had less surface; was not pyrophoric; and readily milled to a clean granular product having a very low proportion of fines.

Example II Employing a spherical-bottomed reactor of the type shown in the drawings having a working volume of 50 cu. ft., an internal 4 diameter and 8 in height, with its perforated plate element placed about 3" above the drain opening, about 40.6 cu. ft. or 4408# of magnesium metal was charged therein. This charging was carried out by filling the reactor with magnesium bars, purging with argon, and melting the charge in place. With the magnesium substantially all melted and subsided at least to the fifty cu. ft. level, titanium tetrachloride was admitted at about 500# per hour. The wall temperature was maintained below 1000 C. by controlling the rate of chloride addition, cooling the furnace with air when necessary, and by adjusting the argon pressure. A total of 15,500# of titanium tetrachloride was prepared for feed to the reaction which amount is equivalent to 90% of the Mg. When 1550# of TiCh were added, the tap valve was opened and the magnesium chloride was witlr drawn at the make rate, which is substantially the same rate of TiCl feed in pounds. The Tick feed rate declined to about 300# per hour when about 70% of the TiCh. had been fed. When all of the TiCl4 had been fed, the reaction was stopped, some additional salt blown out of the drain valve with argon, and the batch subjected to vaccum distillation within the reactor. The cooled titanium sponge thereafter recovered could be handled in air without serious contamination. It Weighed 3700# and occupied a little more than 28 cu. ft. The apparent density of the sponge therefore was 132 pounds per cu. ft. or 47.0% of the ultimate or ingot density of the metal. The weight of titanium produced indicates that of the magnesium was utilized.

Example III Example II was duplicated with the following modifications: 34.2 cu. ft. or 37ll# of magnesium metal was charged to the reactor and melted. Titanium tetrachloride was fed at about 500# per hour. When 260 04% of TiCli had been reacted, the tap valve was opened to drain about 10 cu. ft. of MgClz. When a further 1485# of TiCl4 had reacted, the tap valve was again opened to drain another 10 cu. ft. of salt. This procedure was continued at 1485# addition intervals until 13,000# of TiCh had been reacted. At this point the TiClr was shut off and an eighth increment of salt of about 6 cu. ft. drained. The product titanium metal was purified by vacuum distillation and weighed 3125 having a density of 137 lbs. per cu. ft. Seventy-six cu. ft. of MgClz were drained out or approximately of the total formed.

Example IV Employing the same reactor as in Example II, 28 l9# of magnesium was charged therein and enough titanium tetrachloride was then introduced to react with 90% of such charge. When 40% of the TiCls had been added, intermittent draining of magnesium chloride at approximately the average rate at which it was produced was undertaken and continued until all the TiCLr had been added. After the reaction all available MgClz was drained from the reactor, totaling 75% of that produced. From this operation 2360# of purified titanium sponge having an apparent density of 65 lbs. per cu. ft. was obtained.

In contrast to the results obtained in this invention as illustrated by the foregoing examples, deferring the draining operation in accordance with prior art procedures results in a product having a sponge density of not more than 15% after vacuum distillation and usually about 13% of the ultimate density of titanium. Furthermore, less than 80% utilization of the magnesium is realized and less of the MgClz can be drained with the maximum production attained in the same size reactor (50 cu. ft.) being only about 1900# of titanium. The advantageous benefits which the invention affords over prior methods are shown by the following comparative table:

1 Percent of TiOli consumed when drainage starts.

1 Production capacity for a 50 cu. ft. workmg space.

3 Density .bstoredisbillation related to ultimate density.

Vickers hardness number as determined by well-known Viekers method.

The invention is also applicable to modified methods of operating a batch system for preparing titanium and similar metals. Thus, it is economical to recover the magnesium values and certain volatile titanium values in the volatile products from the distillation step. This can be accomplished by using a reactor previously charged with magnesium bars as the cold end condenser in the vacuum system. The residual magnesium, remaining magnesium chloride, and titanium chlorides are thereby recovered by direct transfer to the subsequent reaction. The reactor containing the Mg bars and the condensate is transferred to the reaction furnace, the Mg melted and titanium tetrachloride reacted and the early draining of MgClz from this reaction, as herein contemplated, is ad vantageously practiced therein. Preferably, as already indicated, the molten salt is valved from the bottom of the reaction vessel starting between the stages of 15% and 50% reaction completion and continuing through any desired subsequent reaction stages. A more limited and very useful application to a batch reaction comprises the removal of by-product molten salt, whileavoiding removal of any appreciable quantity of reducing metal, from the reaction mixtures at a rate such that not more than about 50% of the ultimate by-product salt formed is retained in the reactor at any one time.

Since, under the preferred condition of carrying out the reduction, formation of lower chlorides of the refractory metal being produced is kept at a minimum, the progress of the reaction can in practice be conveniently indicated by measuring the amount of the refractory metal halide consumed relative to the amount of reducing metal in the batch. In practice one can add up to 95% of the chloride calculated to react with the reducing metal. However, to minimize the formation of lower chlorides I usually limit the addition to 90% of theory. It does not appear advantageous to add less than 80% of the theoretical amount.

In carrying out the invention it is only necessary to provide an adjustable draining means at the bottom of the reactor. A conventional type drain pipe and associated control valves will suffice so long as means for melting frozen salt and for interrupt-ing and/ or controlling the flow at the temperatures involved are provided. Draining is facilitated by the use of a perforated false bottom 12 disposed, as shown, above the reactor bottom. The valve means used can consist of a heat-resistant gate valve or it can be the plunger or needle valve type seating upwardly on the outlet orifice. It is convenient to mount a long pointed rod centrally on this plunger to be used in freeing the drain port of frozen salt and small pieces of product metal. Suitable heating means for melting the salt to start flow can be associated with the outlet and valve operating chamber. It is also possible to provide internal cooling means in the plunger to effect solid salt sealing of the port through cooling of the valve parts, and said plunger can be operated by screw means as in the case of normal needle valves. However, it is preferable to use lever operation which gives faster movement of greater amplitude and places the operating controls safely aside from the pouring molten salt.

Whereas certain of the advantages of the invention are realized whenever draining is practiced prior to the 60% point, preferably a marked departure from that critical condition is resorted to and draining is practiced in the earlier stages of the reaction. Broadly, withdrawal of the liquid salt by-product can be commenced at any time prior to that point, a more practical range being to commence the draining operation between about and 50% of the refractory metal chloride consumption. If desired, draining can be started as soon as a small segregated pool of the molten salt collects at the bottom outlot of the reactor. Since there appears to be no easy way of observing this pool, it is practical to keep a safe heel, such as that corresponding to ten percent of the ultimate amount produced, of the salt in the reactor before starting the draining. The actual size of this heel will depend considerably on the size and shape of the reactor. Thus, with a large reactor and a small well near the outlet, draining can begin when as little as one or two percent of the salt has been formed. The placement of bafiles such as the perforated support plate just above the outlet will assist in preventing a salt vortex from drawing molten magnesium down with it. The rate at which the salt is drained after the start can vary considerably. Draining can be continuous or intermittent and, for example, can be conducted in such a manner that not more than 50% of the ultimate salt formed by the reaction is retained in the reactor at any one time. The draining rate can be equivalent to the make rate, or adjusted to leave a definite percent in the reactor, or various arbitrary predetermined schedules can be set up as desired. It has been found that the character of the sponge, such as density and purity, as well as the reaction rate, can be controlled to a considerable extent by the selection of different draining schedules. Preferably, draining is effected according to a schedule which leaves smaller salt residues, since this results in denser form of sponge and provides greater equipment capacity.

At present, the invention finds its greatest application to batch reduction operations, particularly of titanium tetrachloride with molten magnesium. However, it is also advantageously useful in the reduction of other fourth group metal halides (chlorides, bromides, iodides) such as those of titanium, zirconium, hafnium. Chlorides such as ZrCl4, HfCl4, TiClz, TiCla, and mixtures thereof, are particularly effective and therefore preferred for use. Similarly, while reduction of these compounds with magnesium is preferred, other reducing metals, especially those of sodium and calcium, and their mixtures, can also be employed, as can alkali and alkaline earth metals generally. These include, in addition to those mentioned, potassium, lithium, barium and strontium.

The invention applies particularly, as noted, to batch type operations. In the examples the reducing metal charge is placed in an empty reactor. It is also advantageously applicable to multiple type batch operations wherein the reducing metal charge is placed in a reactor containing titanium sponge from previous reduction. Thus, in Example II nearly the maximum practical amount 40.6 cu. ft. of magnesium was used and the rc-' sulting sponge occupied about 28 cu. ft. After draining, as in Example I, more magnesium, either solid or liquid, can be placed in the free space and a second batch reduction performed with a similar application of early salt removal.

Several advantages result from the practice of this invention. The two primary results are a desired great increase in the sponge density and a more complete removal of the by-product salt. These two factors combine to give large economy due to the fact that the product obtained from one cu. ft. of reactor space is greatly increased, to improve the quality of the sponge product and to increase the possible utilization of the reducing metal. These advantages are shown in the examples and are summarized in the above table. The vacuum distillation step is aided because the load of volatile materials to be transferred by distillation is reduced to as low as 40% of that remaining when draining prior to the 60% point is not practiced. This not only eases the distillation load but it increases the overall equipment capacity when the distillate is handled cyclically. The purity of the sponge is improved by the practice of this invention. In the first place, it is less susceptible to con tamination by atmospheric oxygen and nitrogen because of the lower specific surface associated with the denser sponge. In the second place, a rather surprising segregation of impurities contained in the reactant results from the early draining operation. For example, commercial magnesium has an appreciable content of manganese,

eemed iron, ,and oxygen which is undesirably found in the titanium after the reaction. *In some manner not presently well understood, the early draining operation causes these impurities in the magnesium to concentrate in the external portion of the sponge mass, especially in the bottom surface. Consequently, it is possible to remove the iron liner from the' prodnct sponge and mill off a few inches of the surface sponge and obtain an 85 to '95 percent yield of core titanium sponge of unusually high purity. Since it is customary to reduce the massive sponge to a granular state by a milling operation, this stripping of the surface does not constitute a new operation. During milling, there has been a marked tendency to form some very fine material which, due to the tool temperature, picks up nitrogen and oxygen impurities and even exhibits pyrophoric properties causing costly fires. The sponge from this invention does not exhibit these undesirable traits. Still another advantage resulting irorn the greater density of "the drained sponge resides in the increase in capacity of any melting equipment used to reduce the product to ingot-form. Thus, by increasing the sponge density from 15% to 50% of the ingot density, the capacity of the melting vessel is correspondingly increased. Not only is the space requirement per unit weight of the sponge reduced, but the conductivity properties of the metal are improved, re sulting in more rapid and eificient heating by induction and electric arc. It is also feasible to remove the drained sponge from the reaction vessel and purify it, either by vacuum distillation or leaching procedures in special separate vessels. The dense'sponge, wtihits relatively low content of volatile and soluble residues, produced by this invention will require much smaller equipment per pound of product, thereby effecting considerable saving in investment.

I claim .as my invention:

1. A batch process for preparing a fourth group metal selected from the group consisting of titanium, zirconium and hafnium which comprises reducing a volatile halide of said metal with an active metal reducing agent within a closed reactor maintained at an elevated temperature, and when'frorn 1% to not to exceed 60% of the volatile metal halide bcingreduced and necessary in: a complete reaction has been charged from an external source to said reactor, withdrawing fore the reactor molten by product metal halide formed therein.

2. A batch process for preparing a fourth group metal selected from the group consisting of titanium, zirconium and. hafnium which comprises reducingla volatile halide of said metal with an active metal reducing agent within a closed reactor maintained at an elevated temperature. and, when from 15-50% of the volatile metal halide being reduced and necessary for a complete reaction has been charged from an internal source to "said reactor, withdrawing fom the reactor molten lay-product metal halide formed therein.

3. A batch process for preparing titanium metal by; reacting a titanium chloride with a vmolten reducing metal which comprises effecting said reaction within a closed reactor at an elevated temperature and under an inert atmosphere, and removing molten lay-product chloride formed from the reaction mass when the consumption is effected of from 1% to 50% of the ultimate amount of titanium chloride necessary for a complete reaction has been added to said reactor from an external source.

4. A batch process for producing metallic titanium which comprises reacting titanium tetrachloride with molten magnesium within a closed reactor at an elevated temperature and under an inert atmosphere, and draining molten magnesium chloride from the reaction mass and reactor during the reduction reaction when consumption is efifected of from 15% to 50% of the ultimate amount Of'TlClt being reduced and necessary for a complete reaction has been added to said reactor from an external source.

5. A batch process for producing metallic titanium which comprises reacting titanium tetrachloride with molten magnesium within a closed reactor at an elevated temperature and under an inert atmosphere, draining molten magnesium chloride from the reaction mass and reactor during the reduction reaction when completicn of from 15-50% of the TiCL; charge necessary for a complete reaction has been added to said reactor from an external source, withdrawing the sponge metal reaction product in solid form from said reactor, and milling oil the outer surface thereof to recover an 8'595% yield of high purity core titanium sponge.

6. Method for producing titanium metal which comprises forming in a reaction zone of a reactor a pool of magnesium metal and reacting vaporous titanium tetrachloride with said pool in said reaction zone at elevated temperatures to produce titanium metal and molten magnesium chloride and having present throughout the reaction an excess of magnesium metal over the theoretical amount to react with the titanium tetrachloride added, thereby maintaining said pool of magnesium metal in said reaction zone, and for altemate periods during said reaction, repeatedly and continuously retaining therein and draining therefrom magnesium chloride reaction product.

7. Method for producing titanium metal which comprises forming in a reaction zone of a reactor apool of mag-nesium metal and reacting vaporous titanium tetrachloride with said pool in said reaction zone at elevated temperatures to produce titanium meta-1 and molten magnesium chloride and having present throughout the reaction an excess of magnesium metal over the theoretical amount to react with-the titanium tetra-chloride added, thereby maintaining said pool of magnesium metal in said reaction zone, and for alternate periods during said reaction, repeatedly and continuously retaining therein and draining therefrom magnesium chloride reaction product and subjecting said metal to a vacuum distillation purifying operation to remove the volatile impurities therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,763- Maddex June 12, 1951 2,607,674 Winter Aug. 19, 1952 FOREIGN PATENTS 638,840 Great Britain June 14, 1950 OTHER REFERENCES The Mining Journal, July 25, 1952, vol. 239, pages 96.

Claims (1)

1. A BATCH PROCESS FOR PREPARING A FOURTH GROUP METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM AND HAFNIUM WHICH COMPRISES REDUCING A VOLATILE HALIDE OF SAID METAL WITH AN ACTIVE METAL REDUCING AGENT WHITHIN A CLOSED REACTOR MAINTAINED AT AN ELEVATED TEMPERATURE AND WHEN FROM 1% TO NOT TO EXCEED 60% OF THE VOLATILE METAL HALIDE BEING REDUCED AND NECESSARY FOR A COMPLETE REACTION HAS BEEN CHARGED FROM AN EXTERNAL SOURCE TO SAID REACTOR, WITHDRAWING FROM THE REACTOR MOLTEN BYPRODUCT METAL HALIDE FORMED THEREIN.

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