US 2833704 A
Description (OCR text may contain errors)
United States Patent ice PRODUCTION OF TITANIUM Eugene Wainer, Cleveland Heights, Ohio, assignor, by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey No Drawing. Application August 16, 1956 Serial No. 604,343
9 Claims. (Cl. 204-64) This invention relates to the production of titanium metal and more particularly to the preparation of a novel material consisting principally of titanium with minor amounts of carbon and sulfur which is useful in the production of pure titanium by electrolysis of a fused salt bath, in which the novel titaniferous material serves as the source of titanium.
Many electrolytic methods have been proposed for the production of pure titanium metal. which have been recently reported as successfully producing the metal, have involved the use of a fused salt electrolyte and have employed a titanium halide in which the titanium has a valence less than 4 as the source of titanium. Such methods are economically unattractive inasmuch as they require as a preliminary operation the.
preparation of lower valent titanium halides which may be relatively unstable. Furthermore, in the subsequent electrolysis of the titanium halide in a fused salt melt, chlorine or other elemental halogen at relatively high temperature may be evolved with considerable corrosion hazard as far as equipment is concerned, and considerable danger to persons operating such processes. I have now discovered that by substituting a titaniferous material prepared in accordance with my invention as the source of titanium in a fused salt bath used for electrolysis in preparation of the metal, many of the disadvantages of the above identified prior art processes are avoided.
It is one object of this invention to provide an improved cell feed material for the electrolytic extraction of titanium. Cell feed material may, as will hereinafter appear, be either in the form of a consumable anode or it may otherwise constitute one component of the fused bath to be electrolyzed.
This and other objects are readily accomplished by bringing together titanium carbide and a titanium sulfide under suitable reaction conditions.
The titanium sulfide may be any of the simple sulfides such as titanium disulfide, titanium sesqui-sulfide, or titanium monosulfide. The compound approximating titanium monosulfide is preferred in which the ratio of titanium to sulfur is approximately one atom of titanium to one atom of sulfur. The compound may also be a complex or double sulfide of titanium and an alkali metal or alkaline earth metal, and again in this case titanium approximating that in the monosulfide is preferred, namely where the titanium exhibits a valence of two. Thus, in the case of the alkali metal sulfide, a composition approximating the formula Na TiSQ is preferred. When the titanium carbide and the tintanium sulfide are intimately mixed and subsequently heated to an appropriate elevated temperature, the two components react to form the desired cell feed material.
The titanium sulfide may be prepared in a number of ways. It may be produced by reaction between a titanium halide and hydrogen sulfide at a suitable temperature to produce the desired monosulfide. It may also be produced by heating a mixture of titanium dioxide, carbon,
In general, methods 2,833,704 Patented May 6, 19 58 2 and sulfur to very high temperatures. It is possible to produce the simple sulfides by heating mixtures of impure titanium metal, such as scrap, with elemental sulfur under controlled conditions to produce the desired sulfide. Titanium disulfide may be produced by heating titanium dioxide in an atmosphere of carbon disulfide at temperatures in excess of 1500 C. If a mixture of titanium dioxide and carbon is heated in the presence of carbon disulfide, titanium disulfide is also produced. If this product is then heated with titanium carbide under suitable conditions, the monosulfide is produced, and finally heating this monosulfide with titanium carbide produces the impure titanium metal in question. The typical reactions for this latter method of preparation are as fol-- The summation of all the foregoing reactions yields the-following result:
This procedure does not proceed entirely to completion.
so that a rather impure titanium is obtained. If Reaction 2 is carried out in the presence of Na s, the compound Na TiS is formed.
Thus, by choice of suitable starting conditions um sulfides are available in which the valence of the titanium has been completely reduced to 2.
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 with pure carbon under carefully controlled conditions, such that the titanium dioxide is successivelyconverted to Ti O ,Ti O TiO, and finally to TiC, the re.- action of 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 If further purification obtained is substantially pure TiC. is desired, the T10 may be crushed and any extraneous materials separated, leaving a pure TiC suitable for reaction with the titanium sulfide. t In preparing both the titanium carbide, and titaniu sulfide as above described, it will be noted that the starting materials need not be highly purified and this convacuum or in a stream of inert gas such as argon or elium, and add to the melt controlled amounts of titanium carbide proportioned in accordance with the particu- I lar sulfide employed. By maintaining a desired temperature and by removing the carbon and sulfur-reaction products, such as carbon disulfide as they are formed, a
product enriched in titanium and impoverished in both carbon and sulfur may be obtained. For instance, when a titanium carbide which contains approximately by weight of titanium and titanium monosulfide which contains approximately 60% by weight of titanium are, re-"- acted and the carbon sulfide removed as it forms, a prod uct containing an excess of.90% of titanium may be obtained from these starting materials.- The desired end product may also be produced by a solid state reactionand proper methods of preparation simple and complex titani-.
3 at temperatures in excess of 2000' C. This is accomplished by making the reactants available in finely divided form, preferably below 325 mesh. The finely divided mixture is compressed and then heated in a vacuum at temperatures in excessof 2000 C. employing an actively pumping system so as to remove the carbon disulfide as rapidly as formed.
I have further discovered that when such a titanium enriched product is electrolyzed in a fused salt bath, the material deposited at the cathode is of a puritycomparable with the metal obtained heretofore by the electrolysis of a potassium fluotitanate in a fused salt bath. Accordingly, in its broadest aspect, the instant invention comprises a process for the electrolytic production of titanium by the electrolysis of a titaniferous product formed by reacting titanium carbide with a titanium sulfide at elevated temperatures under a controlled atmosphere or a vacuum.
When the titanium carbide and the titanium sulfide are I brought together in suitable portions at elevated temperatures, the carbon and sulfur tend to combine and to form carbon disulfide. By providing means for removing the carbon disulfide as it forms, for instance by operating under a vacuum, or in a system continually swept with a current of inert gas, such as argon, the original TiC-TiS reaction mixture can be continually depleted in carbon and sulfur and enriched intitanium by removal of the carbon and sulfur as a gaseous reaction product.
As indicated, the desired reaction product may be formed by either a solid state or fusion procedure. For example, a mixture of finely divided pure titanium carbide and finely divided pure titanium sulfide will yield, when heated to a temperature of 2000 C. or higher for about one hour in a vacuum or in a current of argon or helium, a regulus of titanium associated with appreciable amounts of carbon and sulfur.
The reactions may be represented as follows:
It is understood that the reactions are never entirely completed. Hence, the titanium obtained is invariably contaminated to some extent with carbon and sulfur.
Practically, the foregoing reactions 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 four hours in a neutral or hydrogen atmosphere. An electrode of titanium monosulfide is similarly prepared at a temperature of 1700 C. An arc is struck between the electrode of titanium carbide and electrode of titanium monosulfide under partial vacuum and the molten drippings are collected while the evolved carbon disulfide is removed by active vacuum pumping.
As a second embodiment, pellets maybe prepared from a mixture of titanium carbide and titanium sulfide proportioned so as to produce the desired final TiSC composition. The pellets may then be fed into the hearth of a water-cooled tungsten arc, water-cooled copper hearth arc melting furnace and melted thereon under an actively pumping vacuum to remove carbon disulfide as generated during the process.
As a further alternative,,consumable electrodes may be are melted to produce the desired alloy. Thus, a powdered mixture of titanium carbide and titanium sulfide proportioned as above may be moistened with moth ylated 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 '4' electrodes in an arc melting furnace from which the carbon disulfide may be removed continuously, as rapidly as it is evolved. Such fusion must take place in an inert atmosphere such as argon or under vacuum conditions.
Having described my invention, following are examples of my method of practice:
Example I In this example, as in all others reported here, the titanium monosulfide was prepared by heating finely di-. vided titanium and elemental sulfur in argon atmosphere under a fixed temperature schedule. The powdered titanium and powdered sulfur were thoroughly mixed and compressed into pellets and placed in a graphite boat. In an atmosphere of pure argon, these pellets were heated first at 500 C. for about 20 minutes at which temperature an evident exothermic reaction took place. The temperature was then raised to between 15GO and l700 C. and maintained at this level for one hour, after which.
the furnace and product were cooled to room temperature in the argon atmosphere. A dense bronzy yellow product was obtained.
From analysis, the product contained roughly 59% titanium and 38% sulfur, the balance being chiefiy carbon and oxygen.
Sixty grams of 325 mesh titanium carbide containing 19.5% carbon and 160 grams of the above -325 mesh titanium monosulfide were compressed into pellets and inserted in the graphite crucible. The crucible and its contents were heated in an induction furnace to 2200 C. under an actively pumping vacuum system and maintained at this temperature for one hour, and then allowed to cool while still maintaining the vacuum to room temperature. The product obtained was a silvery white regulus weighing grams. The approximate analysis of this product was 92.0% titanium, 50% carbon, 2.6% sulfur, and 0.4% others.
Example II Paper tubes are provided approximately /2 inch in diameter and 10 inches in length. Minus 325 mesh titanium carbide containing roughly 19.5 carbon and moistened with methylated spirit was rammed tightly into these paper tubes. These were then stacked lengthwise in a carbon crucible and heatedunder vacuum using an induction furnace to 2000 C. for two hours, after which the crucible and its contents were cooled under actively pumping conditions'to room temperature. The rods were smooth, silvery black in color, and had shrunk to approximately 8 /2 inches in length. Similar rods of titanium sulfide were made in exactly the same manner except that the temperature of sintering was approximately 1700" C. These rods had a silver bronze color.
The rods were positioned in an arc stand on a horizontal plane and the assembly enclosed in a bell jar fitted with a vacuum seal. The are stand hoiders could be manipulated external to the assembly. A water-cooled copper hearth was provided. An arc was struck and feeding rate of electrode manipulated manually. The cooled molten droplets were collected for analysis. The product analyzed roughly 90.2% titanium, 4.1% sulfur, and 5.0% carbon. The relatively high sulfur content appeared to be due to some slight disintegration of the sulfur electrode behind the glowing tip. (The are fusion was started in a third of an atmosphere of argon. As the reaction proceeded, the system was rapidly evacuated and the are continued under roughly to 3 of an atmosphere of carbon disulfide. allowed to cool completely before the bell jar was opened.)
Example Ill Six hundred grams of -325 mesh titanium carbide containing roughly 19.5% carbon and 1600 grams of the titanium monosulfide described in Example I were thor- The reaction mass was argon atmosphere.
oughly mixed and then moistened with methylated spirit, 7
after which they were rammed into a paper tube roughly one inch in diameter and 35 inches in length. In a graphite crucible heated in an induction furnace under actively pumping vacuum conditions, the mixture was heated to between 1800 and l900 C. for about 3 hours, after which the mixture had shrunk in length approximately 12%, in forming a solid rod which later served as an electrode A water-cooled furnace comprising a completely enclosed iron shell was provided having a top arranged to receive the electrode through a closely fitting gland. A valved port was available for connection selectively to either a vacuum system or an argon system. An arc was struck between this electrode and the bottom of the furnace and pumping and water-cooling continued until approximately one-half of the electrode was consumed. At this stage, argon was fed into the furnace, the arc extinguished, and the product allowed to cool under an argon atmosphere. A portion of the product was found to adhere tenaciously to the iron wall and a substantial amount of the deposit was removed by chipping. This product on analysis contained approximately 91% titanium, 3.2% sulfur, and 4.8% carbon.
Exampl IV A fused salt melt was formed by heating 2000 parts by weight of a mixture of equal parts by weight of NaCl and KCl in a graphite crucible provided with a cover having means adapted to maintain a controlled atmosphere within the crucible. A nickel cathode was inserted into the melt and with the crucible serving as anode, an electrolysis was conducted in the cell. The regulus of Example I was broken into small fragments which were fed into the melt at' the start of the electrolysis and which served as the source of the titanium metal to be recovered. With a cell voltage of 2.8 volts and a cathode current density of 100 amperes per square decimeter, titanium was deposited on the cathode at melt temperatures between 775 C. and 850 C. under an The metal recovered had a hardness of 80 Rockwell B and was readily converted into a ductile pellet by are melting in the usual manner.
Example V A consumable electrode of Na TiS was prepared by moistening a fine powder of same with methylated spirits, ramming the moistened product into a paper tube and heating the tube to about (1500 C. in an induction furnace as in Example II. The resulting electrode was reacted with a titanium carbide electrode as in Example 11. The molten drippings were collected below the arc and permitted to cool in the inert atmosphere Within the bell jar. The resulting product, when analyzed, contained 90.8% Ti, 1.8% S, 5.4% C and 2.0% other matter.
The melt illustrated, formed of KCl and NaCl, could, it will be appreciated, be formed of any one or more of the alkali or alkaline earth halides, even though, for
reasons of economy, the alkali metal chlorides are pre-v carbide with a titanium sulfide at an elevated temperature above 1500 C.; removing gaseous carbonand sulfur-containing reaction products from the reaction zone during said reaction, :itil the titanium-sulfur-carbon product formed contains at least about by weight of titanium, and recovering the titanium-sulfurcarbon product formed during said process.
2. The method of producing a product containing titanium, sulfur and carbon, from which the titanium may be readily obtained by electrolysis of said product in a fused salt bath-which comprises: forming an electrode of titanium carbide and an electrode of titanium sulfide; striking an arc between said electrodes and thereby reacting said titanium carbide and said titanium sulfide at an elevated temperature above 1500 C.; removing gaseous carbonand sulfur-containing reaction products from the reaction zone during said arc-reaction; and recovering the drippings constituting a product consisting essentially of titanium, sulfur and carbon and containing at least about 90% titanium, by weight.
3. The method of producing a product containing ti tanium, sulfur and carbon, from which the titanium may be readily obtained by electrolysis of said product in a fused salt bath which comprises: forming a mixture of a titanium carbide and a titanium sulfide; melting said mixture in an arc furnace at an elevated temperature above 1500" C. while removing gaseous carbonand sulfur-containing reaction products from the furnace, continuing the removal of the reaction products until the resulting composition contains at least about 90% by weight of titanium; and recovering the resulting product consisting essentially of titanium, sulfur and carbon.
4. The method of claim 3 in which the mixture is formed into pellets and melted in the hearth of an arc melting furnace.
5. The method of claim 3 in which the mixture is formed into consumable electrodes and melted in an arc furnace.
6. The method of producing titanium which comprises: reacting a titanium carbide with a titanium sulfide at an elevated temperature above 1500 C. while removing gaseous carbonand sulfur-containing reaction products from the reaction zone to produce a product consisting essentially of titanium, carbon and sulfur, containing at least about 90% by weight of titanium; and electrolyzing said product in a fused salt melt, consisting essentially of at least one halide of the group consisting of alkali and alkaline earth halides.
7. The method of producing a product containing titanium, sulfur and carbon from which the titanium 'may be readily obtained by electrolysis of said product in a fused saltbath which comprises: reacting a titanium carbide with a titanium sulfide of the group consisting of simple titanium sulfides and alkali metal-titanium sulfides, at an elevated temperature above 1500" C. and in an inert atmosphere; removing gaseous carbonand sulfur-containing reaction products from the reaction zone during said reaction, until the titanium-sulfur-carbon product formed contains at least about 90% by weight of titanium, and recovering the titanium-sulfur-carbon product formed during said process.
8. The process of claim 7 in which the titanium sulfide is titanium monosulfide (HS).
9. The process of claim 7 in which the titanium sulfide is sodium titanium sulfide (Na Tis