US2681849A

US2681849A - Production of titanium monoxide

Info

Publication number: US2681849A
Application number: US289878A
Authority: US
Inventors: Merle E Sibert; Stuart S Carlton
Original assignee: Horizons Titanium Corp
Current assignee: Horizons Titanium Corp
Priority date: 1952-05-24
Filing date: 1952-05-24
Publication date: 1954-06-22
Anticipated expiration: 1971-06-22

Description

Patented June 22, 1954 UNITED STATES attire PATENT OFFICE PRODUCTION OF TITANIUIVI MONOXIDE No Drawing. Application May 24, 1952, Serial No. 289,878

8 Claims. 1

This invention relates to the production of titanium monoxide and, more particularly, to a method of producing titanium monoxide in a state of high purity substantially uncontaminated by other titanium oxides.

There has been proposed and explored heretofore a method of producing titanium monoxide by reacting titanium carbide with certain metal oxides, such as titanium dioxide, zinc oxide, magnesium oxide and calcium oxide, at temperatures of about 1500 C., the method being described and claimed in copending applications Serial No. 206,712, filed January 18, 1951, and Serial No. 236,476, filed July 12, 1951. The product of this reaction is essentially titanium monoxide, but the product has been found to be contaminated with significant amounts of unconverted titanium carbide and titanium oxides higher than the monoxide. Inasmuch as the primary use of titanium monoxide as a starting material for the production of titanium metal by fused bath electrolysis requires a high degree of purity for the titanium monoxide, the presence of titanium carbide and particularly of higher valence titanium oxides in the titanium monoxide product is undesirable.

In the course of an investigation to ascertain the reason for the presence of unconverted titanium carbide and higher valence titanium oxides in the titanium monoxide produced as described hereinbefore, we discovered that the titanium monoxide is actually produced by two stages of reaction. For example, when titanium carbide is reacted with titanium dioxide, as

described and claimed in copending application Serial No. 289,880, filed May 24, 1952, there is first formed a solid product comprising titanium sesquioxide (Ti2O3) accompanied by the evolution of carbon monoxide. When titanium carbide is reacted with one of the other aforementioned metal oxides, such for example as zinc oxide, as described and claimed in copending application Serial No. 289,879, filed May 24, 1952, a solid titanium sesquioxide product is formed with the simultaneous evolution of carbon monoxide and metallic zinc vapor. Regardless of the specific metal oxide used for reaction with titanium carbide in this first reaction stage, we have found that the second stage comprises reaction between the titanium sesquioxide and previously unconsumed titanium carbide to form solid titanium monoxide with the concomitant evolution of carbon monoxide. We have further found that the first stage reaction proceeds with virtually stoichiometric completion at temperatures within the range of 1000 to 1200 C. and that the second stage reaction proceeds with similar quantitative completeness at temperatures in excess of about 1400 C., whereas there is a pronounced tendency for both reactions to proceed simultaneously when titanium carbide is heated with one or" the aforementioned metal oxides at such an elevated temperature as to produce titanium monoxide in a single heating operation. In such a single heating procedure as that described hereinbefore for the conversion of titanium carbide to titanium monoxide, it appears that some of the mixture of unreacted titanium carbide and other metal oxide is enveloped in an atmosphere of carbon monoxide and that the reaction between the titanium carbide and metal oxide is thereby impeded to such an extent that unreacted titanium carbide and metal oxide are found in the ultimate titanium monoxide product.

In furtherance of our aforementioned investigation, we have discovered that if the two reaction stages are carried out under such conditions that they take place independently and successively, the titanium sesquioxide produced by the first reaction stage can be reacted with a stoichiometric quantity of titanium carbide with the resulting formation of titanium monoxide substantially uncontaminated with titanium carbide or higher titanium oxides. Alternatively, the titanium sesquioxide may be produced by any other procedure and functions satisfactorily in the conversion of titanium carbide to titanium monoxide. Accordingly, the method of producing titanium monoxide pursuant to our present invention comprises forming an intimate mixture composed of substantially stoichiometric amounts of finely divided titanium sesquioxide and titanium carbide, heating the mixture to a temperature of at least 1400 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide. When the titanium sesquioxide is produced by reacting titanium carbide with zinc oxide, magnesia or lime, the over-all process of our invention comprises forming an intimate mixture of finely divided titanium carbide and such a metal oxide, heating the mixture to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide and vapors of the metal of said metal oxide from the residual titanium sesquioxide, and subsequently reacting the titanium sesquioxide with a further quantity of titanium carbide in the manner described here- U inabove. In this two-stage process, the metal vapor removed during the first reaction stage is diluted with less carbon monoxide, and is therefore more readily condensable, than the metal vapor evolved during the single-stage process in which carbon monoxide is evolved simultaneously from both reactions.

The titanium sesquioxide used in the practice of the method of our invention may be produced by oxidation of titanium carbide or by reduction of titanium dioxide, or by any other appropriate procedure. For example, titanium carbide can be so oxidized by heating it at a temperature within the range of 1000 to 1200 C. in intimate admixture with a metal oxide such as titanium dioxide, zinc oxide, magnesium oxide or calcium oxide. The oxidation of the titanium carbide to titanium sesquioxide takes place readily within this temperature range provided an inertatmosphere is maintained. Such an inert atmosphere may be provided either by sweeping the reaction zone with an inert gas such as argon, helium or the like, or by maintaining the reaction zone under a vacuum. Regardless of how the inert atmosphere is maintained, the reaction proceeds with the evolution of carbon monoxide which is withdrawn either with the inert gas which is passed through the reaction zone or by means of the vacuum pumping system. Hence, completion of the reaction is indicated by cessation of the evolution of carbon monoxide. If zinc oxide, magnesia or lime is used as the oxid-ant for the titanium carbide, the resulting vapors of metallic zinc, magnesium or calcium will be evolved and removed with the carbon monoxide. The production of titanium sesquioxide by reduction of titanium dioxide may be carried out readily by heating titanium dioxide, such as pigment grade titania, in a stream of hydrogen at a temperature of about 1500 C. Ex cept for its influence on the purity of the ultimate titanium monoxide, the source of the titanium sesquioxide appears to have no effect upon its reactivity with the titanium carbide.

The titanium carbide used in practicing the method of our invention must also be sufiioiently pure to avoid the introduction of extraneous impurities into the ultimate titanium monoxide. Commercial grade titanium carbide may be used for this purpose provided it is appropriately treated for the removal of iron which constitutes its principal contaminant. The removal of iron may be effected by adding hydrochloric acid to a slurry of the finely divided titanium carbide and subsequently washing the resulting chlorides from the solid titanium carbide. Such a procedure will also remove any metallic iron with which the titanium carbide may be contaminated in the course of a grinding operation in reducing it to a suitable degree of fineness for practicing the invention. Graphite, the other principal contaminant of commercial grade titanium carbide, may either be removed by conventional froth flotation from a slightly alkaline slurry of the titanium carbide, or this graphite may be left in the titanium carbide to be consumed in the reaction zone by incorporating in the reaction mixture a suiiicient additional quantity of titanium sesquioxide to combine with the graphite and thus form additional titanium monoxide and carbon monoxide.

Reaction between the titanium sesquicxide and titanium carbide is promoted by intimate contact between these two reactants. The requisite intimacy of contact may be provided either by a high degree of subdivision of the reactants or by compressing the reactants, and preferably by a combination of these expedients. A suitably fine degree of subdivision is assured when both reactants have a particle size of minus 325 mesh (Tyler standard) and in the case of the titanium carbide we have found it desirable, although not necessary, to grind the carbide in a ball mill or the like to a particle size of about one micron or less. Where compacting of the mixture of reactants is resorted to, particularly satisfactory results are obtained by moistening the mixture with enough water (generally 5 to 10% by weight) as to act as a temporary binder and then compacting the wet mixture into pellets with presssures of about 10 tons per square inch and higher. When the reactants are thus brought into intimate associations with one another, we have found that the reaction proceeds smoothly and substantially quantitatively.

Inasmuch as the reaction between the titanium sesquioxide and titanium carbide proceeds substantially to completion within reasonable reaction periods, the reaction mixture should contain substantially stoichiometric amounts of the two reactants. When the reaction between the titanium sesquioxide and the titanium carbide is preceded by oxidation of another portion of titanium carbide to titanium sesquioxide as described hereinbefore, a stoichiometric excess of titanium carbide in the titanium sesquioxide reaction product may be used in part or in whole as the 'tanium carbide which is reacted with titanium sesquioxide in the practice of our invention. Thus, our method may be carried out by reacting a stoichiometric excess of titanium carbide with a metal oxide such as titanium dioxide, zinc oxide, magnesia or lime under the aforementioned conditions which promote the exclusive formation of titanium sesquioxide, and then heating the residual reaction product, in the same or in a difierent furnace, at a higher temperature pursuant to the present invention for the production of titanium monoxide.

The reaction temperature required in the practice of our invention has been found to be at least 140D C. Temperatures within the range of 1500 to 1750 C. have been found to be particularly advantageous inasmuch as such temperatures promote the complete reaction between titanium sesquioxide and titanium carbide within a period of one hour or less. However, higher temperatures and more prolonged heating periods may be used, the choice of temperature and reaction period being interdependent. Inasmuch as the reaction will proceed with quantitative completeness at temperatures above 1400 0., the reaction period at the temperature used is determined solely by the time required for the reactants to be converted completely to a single residual product composed of titanium monoxide with concomitant evolution of carbon monoxide.

The removal of carbon monoxide during the reaction between the titanium sesquioxide and the titanium carbide is enhanced by the most practical procedures which we have found to be useful in maintaining the necessary inert atmosphere in the reaction zone. For example, we have found that an inert atmosphere may be provided conveniently either by maintaining the reaction zone under a vacuum of 10 mm. of mercury or less, and preferably of about 50 to microns of mercury, or by sweeping the reaction zone with an inert gas suchas argon, helium,

or the like. Both procedures promote the re moval of carbon monoxide from the reaction zone substantially as rapidly as it is evolved, and this removal of the carbon monoxide promotes completion of the desired reaction and the production of titanium monoxide in substantially pure form.

Reaction vessels suitable for the practice of our invention should be constructed of a material which will not be attacked by the reactants or by the reaction products and thereby introduce an extraneous impurity into the residual titanium monoxide. We have found that molybdenum and Hastaloy are suitable materials for the reaction vessel, only a lining of such refractory material being required in that portion of the vessel which holds the solid reactants.

The following examples will serve to illustrate the practice of our invention.

Example I temporary binder and then pelleted under a pressure of about pounds per square inch. The

pellets were heated in a molybdenum-lined graphite crucible in an induction furnace having a starting vacuum of about 50 microns. Heating was carried out at a temperature approximating 1200 C. for a period of 150 minutes. Carbon monoxide and metallic zinc vapor were evolved during this heating period, and the residue was identified by X-ray analysis as being composed essentially of titanium sesquioxide (Ti2O3) containing small amounts of titanium carbide and titanium monoxide.

The titanium sesquioxide obtained as described by the foregoing procedure had a particle size of minus 325 mesh (Tyler Standard). A mixture was prepared of 7.2 parts of this titanium sesquioxide and 3 parts by weight of pure titanium carbide having a particle size of about one micron. The mixture was moistened with water and was pelleted under a pressure of about 10 tons per square inch. The pelleted mixture was then heated in a molybdenum-lined graphite crucible positioned within an induction powered vacuum furnace. The furnace temperature Was maintained within the range of 1400 to 1690 C. over a period of 75 minutes while maintaining a vacuum of about 50 to 60 microns. Carbon monoxide was the sole gaseous product evolved, and the cooled residue from the reaction vessel comprised a golden brown sintered mass which was identified as substantially pure titanium monoxide (TiO).

Example II A mixture composed of 80.0 parts of pigment grade titanium dioxide and 30.0 parts by weight of titanium carbide was moistened with water and pelleted under pressure. The pelleted mixture was then heated under a vacuum of about 50 microns for a period of 60 minutes at a temperature of 1200 C. Carbon monoxide was the only gaseous product evolved during the reacting period. X-ray analysis of the residual product after cooling showed that it was composed of titanium sesquioxide further containing a small amount of a solid solution of titanium monoxide in titanium carbide. The residual product from the first heating operation was again heated under 2. similar vacuum for a further period of 75 minutes at a temperature of about 1550 C. Again, the only gaseous product evolved was carbon monoxide. The residual product, after removal from the cooled furnace, was golden brown color and was identified by chemical, quantitative and X-ray analyses as substantially pure titanium monoxide (TiO).

Example III A reaction mixture was made up of 24 parts of pure titanium carbide and 40 parts by weight of electrically fused periclase (MgO), both reactants having a particle size of minus 325 mesh (Tyler standard). The mixture was pelletized as described hereinbefore and was then heated in an induction furnace under a vacuum of about 50 to 60 microns for a period of minutes at a temperature of about 1200 C. Metallic magnesium vapor and carbon monoxide were evolved during the reaction, and by the end of the reac-. tion period all of the magnesium component of themixture had been removed by distillation. The cooled black reaction product was removed from the furnace and was again ground to minus 325 mesh. The finely ground product was mixed with 6 parts by weight of minus 325 mesh pure titanium carbide and the mixture was again heated in the aforementioned furnace for a period of 75 minutes at a temperature of 1550. C. while maintaining a vacuum of the order of 50 to 60 microns. After cooling of the residual furnace product, it was found to comprise a golden brown sintered material which was identified by X-ray analysis to be substantially pure titanium monoxide (TiO).

Example IV Pigment grade titanium dioxide was reduced to titanium sesquioxide by heating it for a period of minutes at a temperature of 1500 C. in a stream of hydrogen. A mixture of 29 parts of the resulting titanium sesquioxide and 6 parts by weight of pure titanium carbide was then pelleted as previously described and the pellets were heated in a vacuum for a period of 60 minutes at a temperature of about 1500 C. The product removed from the furnace after cooling was identified by X-ray analysis as pure titanium monoxide (TiO). It will be seen, accordingly, that the method of our present invention is marked by its simplicity and that it is particularly characterized by the purity of its end product, titanium monoxide. The method thus lends itself admirably to an integrated process for producing titanium metal wherein the metal is obtained by electrolysis of pure titanium monoxide in a fused salt bath.

We claim:

1. The method of producing titanium monoxide which comprises forming an intimate mixture composed of substantially stoichiometric amounts of finely divided titanium sesquioxide and titanium carbide, heating the mixture to a temperature of at least about 1400 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

2. The method of producing titanium monoxide which comprises forming an intimat mixture composed of substantially stoichiometric amounts of finely divided titanium sesquioxide and titanium carbide, heating the mixture to a temperature within the range of about 1500 to 1750" areas-4e 7 C; in an. inert. atmosphere, removing: therresulting evolved carbon monoxide, and recovering the. resulting residual titaniumnionoxide.

3. The method of producing titaniumv monoxide. whichcomprises forming an. intimate pelleted mixture composed, of substantially stoichiometric amounts offinely divided titanium sesquioxide and titanium carbide, heating the mixture. to a temperature of at least about 1400" C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

4. The method of producing titanium monox ide-which comprises forming an intimatepelleted mixture composed of substantially stoichiometric amounts. of finely divided titanium sesquioxide and. titanium carbide, heating the mixture to a temperature within the range of about 1500 to 1750? C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

5. The method of producing titanium monoxide which comprises forming an intimate mixture of finely divided titanium carbide and a metal oxide of the group consisting of magnesium oxide, zincoxide and calcium oxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the metal oxide, heating the mixture to a temperature within the range of about 1000 to 1200- C. in an inert atmosphere, removing the resulting evolved carbon monoxide and vapors of the metal of said metal oxide from the residual titanium sesquioxide, heating the titanium sesquioxide in intimate admixture with a substantially-stoichiometric. amount of titanium carbide to a temperature in excess of about 1400" C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

6. The method of producing titanium monoxide which comprises forming an intimate mixture of finely divided titanium carbide and a metal oxide of the group consisting of magnesium oxide, zinc oxide and calcium oxide, the amount of titanium carbide being at least stoichiometrically equivalentto' that of the metal oxide, heating the mixture to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide and vapors of the metal of said metal oxide from the residual titanium sesquioxide, heating the titanium: sesquioxide; inintimate. admixture with a substantially stoichiometric amount of titanium carbide to a temperature of about 1500 to 1750" C. in an inert atmosphere,.removing the resultin evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

7. The method of producing titanium monoxide which comprises forming a pelleted mixture of finely divided. titanium carbide and a metal oxideofithe group consisting of magnesium oxide, zinc oxide and calcium oxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the metal oxide, heating the mixture. to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide and vapors of the metal of said metal oxide from the residual titanium sesquioxide, heating. the titanium sesquioxide in pelleted admixture with a substantially stoichiometric amount of titanium carbide to a temperature in excess of about 1400 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the re-- sulting residual titanium monoxide.

8. The method of producing titanium monoxide which comprises forming a pelleted mixture of finely divided titanium carbide and a metal oxide of the group consisting of magnesium oxide, zinc oxide and calcium oxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the metal oxide, heating the mixture to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide and vapors of the-metal of said metal oxide from the residual titanium sesquioxide, heating the titanium sesquioxide in pelleted admixture with a substantially stoichiometric amount of titanium carbide to a temperature of about 1500 to 1750 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the resulting residual titanium monoxide.

References. Cited in the file of this patent UNITED STATES PATENTS Number Name Date 921,686 Fitzgerald et al May 18, 1909 OTHER REFERENCES Titanium, by Jelks Barksdale (1949 ed), pages 94-96, The Ronald Press 00., N. Y.

Claims

1. THE METHOD OF PRODUCING TITANIUM MONOXIDE WHICH COMPRISES FORMING AN INTIMATE MIXTURE COMPOSED OF SUBSTANTIALLY STOICHIOMETRIC AMOUNTS OF FINELY DIVIDED TITANIUM SESQUIOXIDE AND TITANIUM CARBIDE, HEATING THE MIXTURE TO A TEMPERATURE OF AT LEAST ABOUT 1400* C. IN AN INERT ATMOSPHERE, REMOVING THE RESULTING EVOLVED CARBON MONOXIDE, AND RECOVERING THE RESULTING RESIDUAL TITANIUM MONOXIDE.