US2894887A - Production of titanium trihalides - Google Patents

Description

Unimd States Patent C PRODUCTION or TITANIUM TRIHALIDES Anthony J. Kolk, In, South Euclid, and Dwight E. Davis, Hudson, Ohio, assignors, by mesne assignments, to Horizons Titanium Incorporated, Princeton, N.J., a corporation of New Jersey No Drawing. Application February 13, 1956 Serial No. 564,880

5 Claims. (Cl. 204-64) This invention relates to the preparation of compounds of titanium in which the titanium is trivalent. More particularly, it relates to the preparation of titanium trifluoride or titanium trichloride in the form of a product admirably suited to be electrolytically decomposed to yield titanium metal.

Trivalent titanium compounds are assuming increasing importance as raw materials from which titanium metal can be produced. Recently disclosed processes include, among others, the electrolysis of a fused salt bath composed of one or more alkali or alkaline earth metal halides and containing a halide of titanium in which the titanium has a valence of less than four, for example, three or even two.

When a hydrogen halide is passed over titanium carbide at a temperature between about 250 C. and 500 C., we have observed that a titanium 'tn'halide forms on the surface of the titanium carbide, but the reaction ceases after a very short interval of time, probably bccause the trihalide is deposited as a solid, coating the carbide and preventing it from taking part in further reaction.

In accordance with the procedures developed by us, we have found that the titanium carbide may be completely reacted with the hydrogen halide to produce the desired trihalide without the cessation of the reaction previously noted, by suitably controlling the conditions under which titanium carbide and certain hydrogen halides are brought together, we recover a composition containing chlorine or fluorine compounds of the titanium in trivalent form and containing one or more halide compounds of the alkali or alkaline earth metals.

Titanium carbide, hydrogen chloride, hydrogen fluoride and the alkali metal and alkaline earth metal halides are all available commercially of suflicient purity for effecting the desired reaction. It is preferable that the carbide be in finely divided form, e.g. minus 100 mesh (Tyler Standard), or finer. The carbide may, if desired, be readily prepared from titanium dioxide and carbon, in a manner well known in the art. By employing a pigment grade titanium dioxide and pure carbon, a product is obtained substantially free from contamination, except possibly, for small amounts of free carbon.

In our process, finely divided titanium carbide and a material in which the lower valent halide formed will dissolve are disposed in a suitable inert container, such as a porcelain boat in a hot tube furnace or a graphite crucible provided with means to heat the contents thereof; the contents are heated to melt the alkali metal halide or alkaline earth metal halide and then a flow of HCl or HF, to which TiCL; or TiF has preferably been added in a small amount to the HCl or HF, is initiated through the tube or into the furnace, while maintaining the temperature of the charge well above that necessary to melt the alkali metal halide or alkaline earth metal halide.

The following reactions proceed with increasing intensity:

where X represents one or more alkali metals or alkaline earth metals. Up to temperatures of about 600 C., the reaction has been found to proceed at a satisfactory rate. At temperatures above 800 C., the tetrahalide is formed almost exclusively.

As indicated in the above equations, the presence of some tetrahalide is advantageous in suppressing the formation of additional tetrahalide. Care must, however, be taken to avoid adding amounts of the tetrahalide in excess of that which would remain in equilibrium under the reaction conditions, since any excess would tend to react directly with the carbide until the concentration fell to an equilibrium value. The small amount of tetrahalide circulates and is recovered separately and recycled through the system. The hydrogen may be employed to reconstitute additional hydrogen halide, e.g., by burning with chlorine or fluorine, and the carbon may be used to form additional titanium carbide.

Because the reactions are carried out in an environment in which the lower valent halide dissolves, for instance, in a fused salt melt comprised of at least one alkali metal halide or alkaline earth metal halide, the trivalent halide product does not coat the titanium carbide and form a barrier preventing the reaction from proceeding to the complete conversion of the titanium carbide. Preferably the halogen component of the fused melt is the same as that of the hydrogen halide. The fused melt should be oxygen-free and anhydrous and this may be achieved by drying the alkali or alkaline earth metal halide in a current of air heated to about170 C. or by drying the salts at temperatures of about C. under a vacuum.

In the above reactions, the alkali or alkaline earths in the charge form fused baths which are preferably eutectic compositions of two or more alkali or alkaline earth metal chlorides or fluorides, selected so as to provide a stable bath which is molten at temperatures upwards of 350 C. Compositions with suitable melting temperatures may be readily found in the literature. The solid titanium carbide is introduced into the bath as a finely divided particulate material. Once the bath is molten, hydrogen chloride or hydrogen fluoride is introduced into the melt through a suitable inlet tube of graphite or ceramic, provided with a strainer-like plate on the extremity which is immersed in the melt in order to cause the hydrogen halide to be dispersed as it enters the melt. A reaction between the titanium carbide and the HCl or HP promptly ensues with the resultant formation of TiCl or TiF Because the trihalides are soluble or form complexes in the fused melt, they are readily taken upin the melt instead of coating the particles of carbide and hence, the carbide particles continuously present a fresh surface, constantly ready to participate in the desired reaction.

The following examples will further serve to illustrate the features characterizing our invention:

Example I A mixture of 45 parts by weight of dry reagent grade LiCl, 55 parts by weight of dry reagent grade KCl, and 50 parts by weight of TiC was prepared. The mixture of dry ingredients was placed in a graphite crucible which was then placed in a furnace provided with means for admitting gaseous reactants and for discharging the reaction products, as well as with means for maintaining an inert atmosphere therein. The furnace was flushed 3 with dry argon and'the argon atmosphere was maintained throughout the preparation. The mixture was heated until molten and the temperature was thereafter maintained at 450 C. A stream of dry hydrogen chloride was bubbled into the molten mixture through a sparging tube. Some fuming, indicating TiCl formation was noted. After four hours, the reaction was discontinued by terminating the flow of HCl. The salt melt had a faint yellowish green color, characteristic of lower valent titanium. The trivalent titanium amounted to 3% by weight of the melt. The melt containing titanium trichloride produced in this fashion was used to produce metal by electrolysis of the fused melt, by techniques known in the art.

Example I] A mixture was prepared from 500 parts by weight of reagent grade sodium chloride and 100 parts by Weight of titanium carbide. The mixture was placed in a graphite crucible which was placed in a furnace. The furnace was flushed with a dry inert gas, argon, and the argon atmosphere was maintained throughout the preparation. The materials were heated to just above the melting point of sodium chloride. A stream of dry hydrogen chloride was then bubbled into the molten mixture through a sparging tube. The hydrogen chloride sweep was maintained for 3 hours, when the desired concentration of titanium trichloride had been obtained. At the temperature of operation, that is, about 800 C., much of the titanium content is evolved as TiCl Under these conditions of operation about 1.52.0% titanium trichloride was retained in the fused salt. The resultant product was found to be suitable for electrolysis to recover titanium metal as a cathode deposit.

Example III Example I was repeated, using the corresponding fluoride instead of the chlorides. The temperature of operation was. 700 C. Substantially the same results are noted.

We claim:

1. A process for preparing a fused salt composition containing a trihalide of titanium from the group consisting of titanium trichloride and titanium tn'fiuoride and adapted to be electrolyzed to produce titanium metal which comprises: forming an anhydrous melt consisting of at least one halide salt from the group consisting of alkali metal halides and alkaline earth metal halides and which is stable at temperatures above 350 (3.; charging particles of finely divided titanium carbide into said melt while it is maintained molten at a temperature below about 600 (3.; and introducing a halide from the group consisting of HF and HCl into said carbide-containing melt wherein it reacts with the carbide to form the corresponding titanium trihalide in said melt.

2. The process of claim 1 in which an inert atmosphere is maintained over the melt during the process.

3. The process of claim 1 in which the fused salt product containing the titanium trihalide is subsequently electrolyzed to produce titanium metal.

4. The process of claim 1 in which a minor amount of a titanium tetrahalide from the group consisting of TlCl4 and TiF is added to the hydrogen halide being introduced into said melt.

5. A process for preparing a fused salt composition containing titanium trichloride and adapted to be electrolyzed to produce titanium metal which comprises: forming an anhydrous melt consisting of at least one alkali metal chloride and which is stable at temperatures above 350 C.; maintaining an inert atmosphere over said melt; charging particles of finely divided titanium carbide into said melt while it is maintained molten at a temperature below about 600 C.; and introducing hydrogen chloride into said carbide-containing melt wherein it reacts with the carbide to form titanium trichloride in the melt.

References Cited in the file of this patent UNITED STATES PATENTS 1,845,342 Saklatwalla Feb. 16, 1932 2,184,884 Muskat et al Dec. 26, 1939 2,783,142 Singleton et a1 Feb. 26, 1957 FOREIGN PATENTS 141,908 Great Britain Apr. 29, 1920 164,283 Australia Apr. 8, 1954

Claims (1)

1. A PROCESS FOR PREPARING A FUSED SALT COMPOSITION CONTAINING A TRIHALIDE OF TITANIUM FROM THE GROUP CONSISTING OF TITANIUM TRICHLORIDE AND TITANIUM TRIFLUORIDE AND ADAPTED TO BE ELECTROLYZED TO PRODUCE TITANIUM METAL WHICH COMPRISES: FORMING AN ANHYDROUS MELT CONSISTING OF AT LEAST ONE HALIDE SALT FROM THE GROUP CONSISTING OF ALKALI METAL HALIDES AND ALKALINE EARTH METAL HALIDES AND WHICH IS STABLE AT TEMPETATURES ABOVE 350*C.; CHARGING PARTICLES OF FINELY DIVIDED TITANIUM CARBIDE INTO SAID MELT WHILE IT IS MAINTAINED MOLTEN AT A TEMPERATURE BELOW ABOUT 600*C.; AND INTRODUCING A HALIDE FROM THE GROUP CONSISTING OF HF AND HCI INTO SAID CARBIDE-CONTAINING MELT WHEREIN IT REACTS WITH THE CARBIDE TO FORM THE CORRESPONDING TITANIUM TRIHALIDE IN SAID MELT.