US2904426A - Method of preparing cell feed for the fused salt electrolytic production of titanium - Google Patents

Description

WTHOD F PREPARING CELL FEED FOR THE FUSED SALT ELECTROLYTIC PRODUCTION 0F TITANIUM Eugene Wainer, Cleveland Heights, Ohio, assignor, by

mesne assignments, to Horizons Titanium Corporatron, a corporation of New Jersey No Drawing. Original application November 8, 1954, Serial No. 467,581, now Patent No. 2,868,703, dated January 13, 1959. Divided and this application November 6, 1957, Serial No. 694,723

Claims. (CI. 75-10) This invention relates to a thermal method of preparing an alloy consisting principally of titanium with minor but definite proportions of carbon and oxygen, which is particularly useful in the production of pure titanium.

Many methods have been proposed for theproduction of pure titanium metal which may be grouped generally as pyrometallurgical, chemical and electrolytic. Each method suffers from serious disadvantages either as to the raw materials which are necessary, or the temperatures at which the desired reactions take place. Of the three approaches, the electrolytic winning of titanium metal from various compounds appears to ofier the simplest and most economical solution of the problem.

This application is a division of my copending application, filed November 8, 1954, Serial No. 467,581, which issued January 13, 1959, as United States Patent 2,868,703, disclosing and claiming the novel composition of matter adapted to serve as an improved cell feed material from which titanium may be recovered electrolytically and which in turn was a continuation-in-part of an earlier application Serial No. 320,113, filed November 12, 1952, which issued on November 1, 1955, as United States Patent 2,722,509.

In another of my copending applications Serial No. 398,192, filed December 14, 1953, and now abandoned, there is described a process in which titanium is deposited cathodically from a bath in which titanium carbide or mutual solid solutions of titanium carbide and titanium monoxide are chlorinated in situ by suitable chlorinating agents.

In still another copending application Serial No. 398,193, filed December l4, 1953, by John T. Burwell, Jr., and Quentin H. McKenna, and issued as United States Patent 2,876,180 on March 3, 1959, a process is disclosed wherein a transition metal is electrolytically deposited at a cathode from a salt bath prepared by reacting in a fused halide. salt medium, a transition metal carbide or solid solution of transition metal carbide and monoxide such as' those of titanium with a transition metal halide.

It is one object of this invention to provide an improved cell feed material for processes such as those described. The cell feed material may, it will be noted, be a consumable anode, or a constituent of the electrolytic bath, or a material employed in the preparation of the bath.

It is another object of the invention to provide a process for preparing the novel cell feed material.

These and other objects are readily accomplished by bringing together titaniumcarbide and titanium monoxide under suitable reaction conditions. Inasmuch as titanium carbide and titanium monoxide have the same cubic structure and spacegrouping and nearly the same lattice size, they are capable of forming a continuous series of solid solutions ranging from pure titanium carbide to pure titanium monoxide. intimately mixed and subsequently heated to an appropriate elevated temperature under a reduced pressure, the

two components form a mutual solid solution from which,

When the individual components are 2,984,426 I Patented Sept. 15, 1959 ice because of the reduced pressure, carbon monoxide tends to be eliminated.

The titanium carbide employed may be prepared by any of a number of well-known processes. It may be produced by reacting pure or pigment grade titanium dioxide (TiO in finely divided form (-325 mesh Tyler Standard) with pure carbon (prepared by calcining lampblack) under carefully controlled conditions so that the titanium dioxide is successively converted to T i 0 Ti O TiO and finally to TiC, the reaction at each of the stages taking place between solid materials. The amount of carbon employed should be slightly in excess of the stoichiometric amount required for the complete conversion of TiO;, to TiC. The product obtained is substan-- tially pure TiC. If further purification is desired the TiC may be crushed and any extraneous materials separated leaving a pure TiC suitable for reaction with the titanium monoxide.

The titanium monoxide may be prepared in any known manner. It may be prepared from titanium carbide in the manner taught in each of US. Patents 2,681,847, 2,681,848, or 2,681,849. I prefer to follow the practice described in United States Patent 2,750,259 wherein a process is disclosed in which titanium dioxide (TiO is converted first to titanium sesquioxide (Ti O and the sesquioxide is further reacted to produce titanium monoxide (TiO).

In preparing both the titanium carbide and the titanium monoxide as above described, it will be noted that the reactions occurred between materials in the solid state, and it will be further noted that there are obtained relatively pure compounds of titanium and oxygen or titanium and carbon by carrying out the reactions under carefully controlled conditions.

Although I presently prefer to use the pure carbide and the pure monoxide as starting materials for making the desired reaction mixture, the carbide and the monoxide may be somewhat impure without impairing the effectiveness of the process constituting my invention. Thus the carbide may contain some titanium oxide and the monoxide may contain some residual carbon or titanium carbide.

I have now found that titanium carbide and titanium monoxide may be reacted with one another to produce therefrom a product enriched in titanium content together with small amounts of carbon and oxygen. Essentially my method comprises melting titanium monoxide (TiO) in a vacuum or partial vacuum and adding to the melt controlled amounts of titanium carbide (TiC). By maintaining the temperature above the liquidus for the system Ti-TiO-TiC, and by removing carbon monoxide as rapidly as it is formed, a product enriched in titanium and impoverished in both carbon and oxygen may be obtained. For instance, by adding titanium carbide (which contains approximately 20% carbon) to molten titanium monoxide (which contains about 25% oxygen) and removing the carbon monoxide as it forms, a product containing in excess of 90% titanium may be obtained from starting materials with between and titamum.

The foregoing reaction may be accomplished in many ways. In a preferred embodiment of the invention the TiC prepared as above indicated is moistened with methylated spirit, shaped in the form of an electrode, and baked at a temperature of about 2100 C. for 4 hours.

. An electrode of TiO is similarly prepared at a temperature of 1700 C. An arc is struck between an electrode of titanium carbide and an electrode of titanium monoxide under partial vacuum and the molten drippings are collected while the evolved carbon monoxide is removed by active vacuum pumping.

As a second embodiment, pellets may be prepared from a mixture of titanium carbide and titanium monoxide proportioned so as to produce the desired final Ti-OC composition. The pellets may then be fed into the hearth of a water-cooled tungsten are, water-cooledcopper hearth arc melting furnace and melted thereon under an actively pumped vacuum to remove carbon monoxide gas generated during the process.

As a further alternatlive, consumable electrodes may be are melted to produce the desired alloy. Thus a powdered mixture of titanium carbide and titanium monoxide proportioned as above may be moistened with methylated spirits and then pressed or extruded into the form of pencils suitable for use as electrodes and then baked or partially sintered. The rods so obtained have an excellent conductivity and may be used as consumable electrodes in an arc-melting furnace from which carbon monoxide may be removed continuously, as rapidly as it is evolved. I

The novel titanium, carbon and oxygen products of this invention are readily formed by bringing together at temperatures above the melting point of TiO (1750 C.) pure titanium carbide and pure titanium monoxide 1n suitable proportions, consistent with the temperature and pressure of operation to yield the described alpha titanium alloy with oxygen and carbon containing a small amount of a second phase, presumably TiC. While I do not wish to be bound by any specific theory as to what occurs, one possible explanation for the reaction may be oifered based on the phase diagrams for three binary systems Ti-TiO, Ti-TiC, and TiOTiC, and the melting points for the ternary system TiOC represented as Ti-TiO-TiC.

Starting with a mixture of TiO and TiC in equimolar proportions in an arc furnace, as the temperature is raised, the TiO melts at 1750 C. and TiC gradually dissolves in the TiO as shown by the liquidus line of the T iO-TiC quasi-binary. Carbon monoxide is formed by the reaction between TiO and TiC and is removed by the vacuum pump, changing the over-all composition toward the titanium cor er of the ternary diagram. As the composition is progressively depleted in carbon and oxygen and correspondingly enriched in titanium, the melting point gradually follows the liquidus-surfaces in the ternary diagram. When suflicient carbon monoxide has been removed, the oxygen content of the system is lowered to such an extent that the over-all composition falls within the alpha region of the TiTiO binary. In equilibrium at this time are 1) alpha titanium, saturated with oxygen, and (2) titanium carbide. Further removal of carbon monoxide through the active vacuum pumping permits the oxygen content to be further lowered to a value determined by the temperature, pressure, and carbon content. Eventually an alloy of titanium is produced consisting of alpha titanium saturated with oxygen as one phase and gamma TiO C as a second phase. In the specific instance cited, i.e., starting with a mol-mo-l mixture of TiO and TiC analyzing 12.9% 0, 9.7% C and 77.4% Ti (all weight percents), I have obtained an alloy analyzing 5.2% O, 5.5% C and 89.1% Ti by weight. In the system, this would represent an alloy of alpha titanium saturated with respect to oxygen and carbon whose total weight is equal to 97.7% of the composition, the remaining 2.3% being free titanium carbide.

In general, the products obtainable by my process have been found by analysis to contain from 89% to 92% titanium, from 2.5% to 5.5% carbon, and from 1.5% to 5.5% oxygen, depending on the temperature at which the molten mass was held, the proportions of TiC and TiC employed, the degree of vacuum, and the length of time the molten mass was held at temperature.

The following additional examples will serve to further illustrate my invention:

Example I Titanium carbide of 325 mesh particle size (Tyler Standard) analyzing 78.1% Ti and 21.7% C, and TiO of -325 mesh particle size (Tyler Standard) analyzing 73.3% titanium, 2.2% carbon and 24.0% oxygen, were blended in equimolar proportions, based on stoichiometric combination of available carbon and oxygen. The mixture was pressed into a 20 gram pellet at 20 tons per square inch without the use of a binder.

The pellet was fused in the electric arc in an atmosphere of 15 inches (mercury) or argon. Reaction was continued until fuming stopped and the charge had c0- alesced into a round button.

The button, when cooled, was silvery in color. Chemical analysis indicated titanium and carbon content of 89.5% and 5.9% respectively. Vacuum fusion analysis indicated an oxygen content of 4.4%.

Example II Titanium carbide of 325 mesh particle size (Tyler Standard) analyzing 78.1% titanium and 21.7% carbon, and titanium monoxide of '-325 mesh particle size (Tyler Standard) analyzing 73.3% titanium, 2.3% car'- bon, and 24.0% oxygen, were blended in a proportion calculated to provide an excess of 1.5 weight percent carbon over the amount of carbon required to combine stoichiometrically with the oxygen.

The material was pelleted and fused as in the preceding example. Chemical analysis indicated titanium and carbon contents of 91.6% and 4.7% respectively. Vacuum fusion analysis indicated an oxygen content of 3.4%.

The high titanium alloys of this invention containing oxygen and carbon are distinguished from other prior art titanium-oxygen-carbon compounds by their extremely high titanium content. For example, Kinz'ie and Hoke in US. Patent 2,040,854 reported a product correspondingto the formula Ti OC with a titanium content between 67% and 69%, While in US. Patent 2,129,161, Kinzie and Wainer describe a substance containing about 65.5% Ti corresponding to Ti OC Other substances such as TiOC containing 63.3% Ti and Ti OC containing 77.4% Ti are also known, but none of these prior art materials is as rich in titanium as the product of my process which is hexagonal close packed titanium containing some oxygen and carbon as the major phase, with a small amount of titanium carbide as the minor phase.

By virtue of its high titanium content, my product is peculiarly adapted to be employed as the cell feed material in an electrolytic process for the production of titanium. As a cell feed material it may find application in any one of several ways. For example, an anode formed of the titanium-oxygen-carbon product of this invention may be caused to give up its titanium which is transported through the fused bath to the cathode where it is deposited, in accordance with the process described and claimed in my application Serial No. 320,113, which issued on November 1, 1955, as Patent 2,722,509. As another alternative, the titanium-oxygen-carbon product of my invention may be added to a fused halide salt bath and reacted therein with chlorine to produce a bath which on electrolysis yields a deposit of titanium at the cathode, in accordance with the continuous process described and claimed in my copending application Serial No. 398,192. Other uses will readily suggest themselves to those skilled in the art, it being obvious that the product of this invention may be used as a starting material for the preparation of titanium compounds as well as for the electrolytic recovery of titanium.

I claim:

l. A method of preparing a cell feed material suitable for the electrolytic recovery of titanium'and containing between 89% and 92% titanium by weight comprising: melting titanium monoxide, adding titanium carbide to the melt, maintaining the resulting compositionevolved from the melt, continuing the addition of titanium carbide and the removal of carbon monoxide until the melt has been enriched to a titanium content between 89% and 92%, and recovering the so enriched titanium product.

2. The method of claim 1 in which the titanium monoxide is melted under a reduced pressure.

3. A method of preparing a cell feed material suitable for the electrolytic recovery of titanium and containing between 89% and 92% titanium by weight comprising preparing a mixture of finely divided titanium monoxide and finely divided titanium carbide, proportioned to contain between about 75% and 80% titanium, as monoxide and carbide, by weight, pelleting the said mixture, melting the pellets in an inert atmosphere in an arc furnace, maintaining an inert atmosphere in said furnace and maintaining a pressure of less than one atmosphere in said furnace, removing carbon monoxide as it is evolved from the melt, maintaining the melt molten until the resultant product is enriched to a titanium content of between 89% and 92%, by weight, and depleted in carbon and oxygen and recovering the so prepared product.

4. A method of preparing a cell feed material suitable for the electrolytic recovery of titanium and containing between 89% and 92% titanium by weight comprising 25 preparing a mixture of finely divided titanium monoxide and finely divided titanium carbide, proportioned to contain between about 7 5% and 80% titanium, as monoxide and carbide, by weight, shaping the mixture into the form of electrodes, consuming the electrodes in an arc furnace as consumable electrodes, maintaining an inert atmosphere in said furnace and maintaining a pressure of less than one atmosphere in said furnace, removing the carbon monoxide as it is evolved during the consumption of the electrodes, and recovering the product.

5. A method of preparing a cell feed material suitable for the electrolytic recovery of titanium and containing between 89% and 92% titanium by Weight comprising preparing an electrode of titanium carbide, preparing an electrode of titanium monoxide, striking an are between the said electrodes and collecting the molten product thereof while continuously removing any carbon monoxide evolved during the arcing and melting, maintaining the molten product under an inert atmosphere having a partial pressure of carbon monoxide less than one atmosphere and recovering the resultant product depleted in carbon and oxygen and containing between 89% and 92% by weight of of titanium.

References Cited in the file of this patent UNITED STATES PATENTS 1,523,103 DAdrian Ian. 13, 1925 2,205,386 Balke et al. Jan. 25, 1940 FOREIGN PATENTS 754,981 Great Britain Aug. 15, 1956

Claims (1)

1. A METHOD OF PREPARING A CELL FEED MATERIAL SUITABLE FOR THE ELECTROLYTIC RECOVERY OF TITANIUM AND CONTAINING BETWEEN 89% AND 92% TITANIUM BY WEIGHT COMPRISING: MELTING TITANIUM MONOXIDE, ADDING TITANIUM CARBIDE TO THE MELT, MAINTAINING THE RESULTING COMPOSITION UNDER AN INERT ATMOSPHERE AND UNDER A PRESSURE OF LESS THAN ONE ATMOSPHERE, MAINTAINING THE MONOXIDE MOLTEN WHILE CONTINUOUSLY REMOVING THE CARBON MONOXIDE EVOLVED FROM THE MELT, CONTINUING THE ADDITION OF TITANIUM CARBIDE AND THE REMOVAL OF CARBON MONOXIDE UNTIL THE MELT HAS BEEN ENRICHED TO A TITANIUM CONTENT BETWEEN 89% AND 92%, AND RECOVERING THE SO ENRICHED TITANIUM PRODUCT.