US2812250A - Production of titanium by the reduction of titanium tetrachloride by magnesium - Google Patents

Description

-: 2,812,256 Patented Nov. 5, we?

PRODUCTION OF TITANIUM BY THE REDUC- TION OF TITANIUM TETRACHLORIDE BY MAGNESIUM William H. Dietz, Marshallton, Del., assignor to E. I. du Pont de Nemours and Company, Wiimington, Dela, a corporation of Delaware No Drawing. Application September 29, 1952, Serial No. 312,173 a 2 Claims. (Cl. 75-84.5)

products of the reaction are moltenmagnesium chloride and titanium metal in the form of a spongy mass which extends through the salt phase and contacts the walls of the reactor. Since titanium forms alloys with practically all structural metals at elevated temperatures, it has been found that ferrous'metal reactors are most feasible with respect to cost and 'the results obtained. Because of the alloying tendency, the Wall temperature of the reactors are controlled at about 950 C. to minimize the alloying or inter-diffusion of the titanium with the ferrous metal. The desirable properties of pure titanium for many uses are destroyed by small amounts of iron. Furthermore,

the alloying has a marked destructive effect on the apparatus. This has been, in part, the reason for providing thin disposable iron liners in the expensive alloy steel reaction vessels.

Although the melting point of the titanium iron alloy system has a minimum of about 1050' C., a marked degree of difiusion occurs at 950 C. In large scale commercial equipment it is difficult to dissipate the large amount of heat formed by the reaction at a satisfactory rate and still hold the wall temperature below 950 As a result, considerable iron is found at the surface of the sponge mass and a significant portion of the sponge must be cut off and discarded.

An object of this invention is to provide a means of decreasing the inter-diffusion of the refractory metal product with the structural metal or 'metal liners ofthe reactor in which it is prepared. Further objects are to improve the yield and purity of the titanium and to assistin the preservation of the reaction Vessel. These objects r a ta ne in net lotherm s processes for the reduction of ch ri e o the ref ac ory me als of subg oup V A of e p rio i abl y the mor ac e alkali an alkaline a th m a ncluding m gn um) by my inven i n whic ompri e pr or o the iniat n of the redu i reaction, coating inner surfaces of the reaction vessel, hi h uld oth rw s com i o nt mate c ntact with the so i refracto y m al produ t, with a carbona eous layer and heat treating, Preferably under vacuum, to remove volatile constituents of the coating.

Specifically, these objects are attained in the metallothermic reduction of titanium chloride by coating prior to initiating the reduction reaction, inner surfaces of the reaction vessel, which are to come in contact with the solid titanium metal sponge, with a carbonaceous layer, and heat treating, preferably under vacuum, to remove volatile of the reactor.

constituents of the coating such as solvents, oils, water, hydrogen, and the like.

More specifically, the interior of the reactor or its liner is coated prior to initiating the reduction reaction by simple'means such as'brushing, spraying, or Wiping with a dispersion of carbon particles in a relatively volatile liquid, heating in vacuum or a stream of inert gas such as argon to eliminate the liquid. I

A preferred method comprises coating the inner reactor surfaces with a thin dispersion of graphite in water, drying and heating in vacuum, proceeding with the metallothermic reduction reaction without exposing the treated interior to air or moisture, draining away the molten byproduct salt and subjecting the charge to vacuum at about 1000 C. to distill out residual volatile substances such as MgCl Mg and titanium chloride.

This invention has been found successful in batch re- The bottom of the reactor is spherical or conical and car-.

ries a central bottom outlet pipe. The inner surface is protected .by a removable sheet iron liner which is open at the top and conforms to the inner contours of the reaction vessel. The liner also carries a central discharge pipe at its bottom which passes coaxially through the bottom pipe These concentric pipes are united or sealed at the annulus preferably by Welding. The central discharge pipe of the liner, through which the liquid magnes-ium chloride may be withdrawn, is closed by a conical metal piece seating upwardly within the pipe opening and acting as a valve to control the flow. The whole assembly is lowered into an electric pot furnace which may also be cooled as desired by circulating air. The liner is also advantageously provided with a perforated support plate near the bottom which assists in draining the salt away from the titanium sponge. According to this invention the inner'surface of the liner, including its perforated false bottom is coated with carbon, usually in the form of graphite. When the reduction reaction has been completed, the available molten salt has been drained out and after the residue has been subjected to vacuum distillation to remove remaining salts and magnesium, the vessel after being cooled is opened, the bottom pipes cut apart and the liner and its charge of titanium sponge withdrawn. The liner is cut, stripped from the sponge and discarded.

In a preferred mode of operation the carbon-treated vessel is charged with magnesium bars or ingots heated to about 400 C. during evacuation to purge volatiles from the carbon film, flushed with argon and then connected to the vacuum distillation conduit of another reaction vessel'containing the drained reaction product from a previous reduction. The system is then evacuated and the vessel containing the reduction product along with the connecting conduit is heated to about 1000 C., while the newly treated and charged vessel is cooled. During this distillation operation some magnesium chloride, some magnesium and probably some titanium chlorides are condensed in the cooled vessel. This vessel is then disconnected under protection from the air and moisture and placed in a reaction furnace. The reduction of more titanium is then carried out in this vessel according to the process previously described but in the presence of the condensate from the previous reduction. Specific applications of this invention and the results obtained are illustrated in the following examples:

3 4 EXAMPLE I Table II A cylindrical reaction vessel, such as that just described, was assembled with a steel liner serving to pro- Protected ,;3g, tect the interior of the vessel from the reactants. The 5 steel liner and upper surface of the perforated plate were Percent Ironum .22 coated with a film of colloidal graphite dispersed in water, Percent Nitrogen. .01 .012 the amount of carbon being deposited on the liner surgiiiiiii ri a iiifi iw iii face varying between one and five grams per square foot of coated area. The vessel was then charged with 1500 pounds of magnesium metal ingots and a suitable cover f i m i f f I l Product. from the carbon-protected bolted on. The water from the film was removed by Showm me higher quahty vacuum heating. The vacuum was then let down with EXAMPLE III argon and i .Vessel further.heated to melt h g The cylindrical reaction vessel previously used was asneslum' Tltamum tetlaqhlonde was admltt? to sembled with a steel liner serving to protect the interior the reactor at a rate hunted y the speclfieii maxmlmm of the vessel from the reactants. Over one-half the side wall FP F of aboui 950 From tune to of the liner was spread a thin layer of colloidal graphite as the lnanwm tiatrachlonde was added the by'product dispersed in water, the carbon deposit on the liner being magneslum chloride was tapped from the bottom of the approximately 3 grams/Sqft and the other half was When about elghty'five Rercent of the left uncoated. The assembled vessel and liner was then 35 had bee.n g l g g all charged with magnesium as before and a suitable cover fij i igifg s x g g 523 31 gg i g z; bolted on. Vacuum heating was then applied to remove distill off the major portion of the remaining magnesium the wamr dlspersmg med-1 Follow-mg this treatm-ent chloride magnesium and some titanium chlorides After the vessel was eaied until the mggnesmm was esse-nnany dist llation the char e was cooled the liner removed molt-en and tltamum chlonde Introduced: As m the frorh the geactor d peeled from titanium p g previous examples, molten salts were drained from the bottom of the vessel, and the contents subjected to vacuum The titanium was then milled to about one-inch particles and leached to remove the last residues of salt and magdlstluatlon poled an? dl-scharge-d' nesium The analytical data for the washed and dried The essentlany (Eylmdncal finished mass of tltamum finished product is shown in the table in comparison with sponge was then mllled-from the to a flat fac? about the product from a batch processed similarly except that half Way down the cyhnder' Dnnmgs and tummgs it was not protected by a diffusion barrier placed on the sponge Were-then-taken from the two halves of the cyhnliner wall der at varying distances from the edge so as to have samples of metal protected by the difluslon barrier as well Table l as metal not so protected. Analyses and tests of samples are shown in Table III which demonstrates the advantages Protected of the invention.

Protected Table 111 Percent Iron .05 .20 40 IRON CONTENT 1 35.33 diiilifi it it Brlnell HardnessII iao 145 Protected $225M Turnlngs Outer percent 0.20 2. 7 It is seen that the carbon protection served to give a g gll g'ffg edggm M06 purer product and one of greater ductility (lower hard- Q111 35: iii EdZfiII do 818% 81 ness).

CARBON CONTENT A similar steel reaction vessel was assembled with a fi 9gg "Percent" 9 8? 9 steel liner serving to protect the interior of the vessel from Drillings 2%" from edge" 0. 009 0. 007 the reactants. A light volatile oil dispersion of finely di- Drillings fmm edge M09 vided graphite was applied to the steel liner, the carbon deposit being approximately 2 grams/sq. ft. The vessel BRINELL HARDNESS was then charged with 1500 pounds of magnesium and a cover bolted in place. Vacuum heating to remove the ggrgggfi gggfi hgnt volatile oil was then carried out. Following this Drillings 2%" from edg 130 147 heating, the vessel was connected to a previously reduced Drmmgs fmm edge 127 batch and used, as hereinbefore described, to receive the condensate from the distillation step. After discon- The type of carbon used to coat the vessel or liner may nectmg and transferring to the reduction furnace the vary. For example carbonaceous material such as pitch magnesium was melted and titanium chloride addition or tar may be diluted with solvents, spread on the surface started. From time to time magnesium chloride was and baked on, preferably under vacuum to leave only tapped from the bottom of the vessel. When about 85% carbon in the film. Thick coats are not desirable since of the total magnesium had been utilized, the titanium 0 they tend to scale 01f on drying and baking resulting in carchloride addition stopped and magnesium chloride was bon contamination of the product. It is also preferred to removed as far as possible by drainage. Following drain use rather fine carbon since it appears to make a more age the vessel was sealed, heated to about 1000 C., for impervious barrier and adheres better than coarse maslx hours while being evacuated. terial. The known commercial suspensions and disper- After vacuum distillation of impurities the sponge sions of garphite in water or in oil are eminently suited titanium was removed from the liner and the size reduced for this use and are usually preferred. Minimum amounts by crushing. Analysis of the finished batch is shown in of carbon compatible with securing a complete coating Table II along with the analysis of another batch, procare desired. Thus, where operating conditions permit slmllally Pt that no graphite protection diffusion careful application, I may use as little as 0.1 gm. per barrier was placed on the liner.

square foot of finely divided graphite and obtain improved results. However, in practice it is usually best to apply from 1 to 5 grams of carbon per square foot to insure complete coating.

The carbon coating may be applied in a separate operation if desired. Thus, the liners may be pro-treated and vacuum baked prior to installation. However, I prefer to bake them out after the reactor is charged with magnesium and closed thus avoiding adsorption of atmospheric contaminants such as water, oxygen and nitrogen. The reactor surface may also be coated by simple rubbing with solid graphite. The baking temperature is not critical and in practice may run as high as 1000 C., but lower temperatures and high vacuum adapted to removal of, for example, water from the aqueous film are preferred. When non-volatile residues, such as hydrocarbon pitches, are used the higher temperatures are desired to crack the compounds to elemental carbon.

It is believed that carbon imposes a high melting film between the two metals which is sufliciently impervious to effectively prevent inter-diffusion. Perhaps the flakelike structure of graphite with the accompanying possibility of leafing provides a superior film. It may be that a portion of the barrier consists of high melting titanium or iron carbide. It is thought, however, that the carbide formation at the temperatures used is rather slow and that the carbon itself forms the main barrier. Regardless of the foregoing theoretical considerations the simple step of providing the carbon film serves to give the desired barrier. Although this invention has been found applicable to the production of titanium, it is also of great advantage in the preparation of other similar metals such as zirconium and hafnium, especially when the process involves the metallothermic reduction of the refractory metal chlorides in ferrous metal containers which become otherwise intimately contacted with the refractory metal product. Magnesium is the currently preferred reducing agent in the preparation of these metals, but other of the more reactive metals, more electropositive than the metal being produced, namely the alkali metals and alkaline earth metals which term is considered to include magnesium are effective in this invention and in instances of their use the carbon barrier of this invention is also advantageous. For economic reasons the most useful reducing metals will be magnesium, sodium and possibly calcium. Since liquid alkali metals, especially potassium, have a tendency to disintegrate graphite, it is preferable to use non-graphitic carbon in cases where molten potassium or sodium, or other alkali metal is the reducing metal in contact with the treated vessel. In instances where sodium or other alkali metal is fed simultaneously with the refractory metal chloride the graphite barrier may be used.

The refractory alloys of titanium such as those with molybdenum, zirconium, tungsten and the like may also be protected from ferrous contamination by this invention when produced by co-reduction methods. Additionally, the invention may be used in the coating of reaction vessels other than those made of steel as mentioned in the above examples. The carbon coating may be applied to other metal surfaces as for examples stainless steel, nickel, molybdenum, tungsten and the like and the fourth group metal being produced or treated in containers of such structural metals are likewise maintained in the purified state.

The advantages of this invention are primarily related to the quality of the product as hereinbefore explained. This carbon film does also improve the ease of peeling the disposable iron liner from the sponge. Similarly, the application of the carbon barrier to an unlined ferrous metal reactor provides a better line of demarkation between sponge and reactor thereby assisting in the separation of the two by a milling or boring operation. Protection of the reactor is an important advantage here. A further advantage lies in the fact that one does not have to watch the reactor wall temperature quite so closely. This means that higher reduction rates are possible and that higher average distillation temperatures may be advantageously used.

I claim as my invention:

1. A process for the production of titanium metal in a closed reaction vessel having its inner wall surfaces in contact with the titanium product coated with from 1 to 5 grams per square foot of carbon spread over said surfaces as a film in the form of a liquid suspension, comprising charging said vessel with magnesium, heating and evacuating the vessel to remove volatile constituents present in said film, admitting titanium tetrachloride to the vessel for reaction with said magnesium while maintaining the walls of said vessel at a temperature of about 950. C., draining from said vessel a major portion of the magnesium chloride reaction by-product which forms, evacuating said vessel and heating it to between 900 and 1000 C. to distill off and remove residual magnesium and magnesium chloride, and recovering the resulting titanium metal product.

2. A process for the production of titanium metal which comprises providing a sheet iron liner for the interior walls and bottom of a closed reaction vessel, the inner surfaces of which liner are coated with from 1 to 5 grams per square foot of graphite spread over said surfaces as a film in the form of a liquid suspension, comprising charging said vessel with magnesium, heating and evacuating the vessel to remove the volatile constituents of said graphite film, admitting titanium tetrachloride to said vessel for reaction with said magnesium while maintaining the 'walls of said vessel at a temperature of about 950 C., draining from said vessel a major portion of the magnesium chloride reaction by-product which forms, evacuating said vessel and heating it to between 900 and 1000 C. to distill OE and remove residual magnesium and magnesium chloride, and recovering the resulting titanium metal product.

References Cited in the file of this patent UNITED STATES PATENTS 243,788 Pedder July 5, 1881 2,091,087 Wempe Aug. 24, 1937 2,205,854 Kroll June 25, 1940 2,245,747 Barr June 17, 1941 2,246,463 Garrott June 17, 1941 2,262,220 Bennett et al. Nov. 11, 1941 2,423,898 McLain July 15, 1947 2,493,642 Renshaw et a1. Jan. 3, 1950 2,548,897 Kroll Apr. 17, 1951 2,551,341 Scheer et a1. May 1, 1951 2,564,337 Maddex Aug. 14, 1951 2,567,838 Blue Sept. 11, 1951 2,616,800 Wortman Nov. 4, 1952 2,618,032 Traenkner Nov. 18, 1952 2,647,826 Jordan Aug. 4, 1953 2,663,634 Stoddard et al. Dec. 22, 1953 2,694,653 Loonam Nov. 16, 1954 FOREIGN PATENTS 4,295 Great Britain of 1882 OTHER REFERENCES The Mining Journal, July 25, 1952, vol. 239, pages -96, article by Oldham.

Claims (1)

1. A PROCESS FOR THE PRODDUCTION OF TITANIUM METAL IN A CLOSED REACTION VESSEL HAVING ITS INNER WALL SURFACES IN CONTACT WITH THE TITANIUM PRODUCT COATED WITH FROM 1 TO 5 GRAMS PER SQUARE FOOT OF CARBON SPREAD OVER SAID SURFACES AS A FILM IN THE FORM OF A LIQUID SUSPENSISON, COMPRISING CHARGING SAID VESSEL WITH MAGNESIUM, HEATING AND EVACUATING THE VESSEL TO REMOVE VOLATILE CONSTITUENTS PRESENT IN SAID FILM, ADMITTING TITANIUM TETRACHLORIDE TO THE VESSEL FOR REACTION WITH SAID MAGNESIUM WHILE MAINTAINING THE WALLS OF SAID VESSEL AT A TEMPERATURE OF ABOUT 950*C., DRAINING FROM SAID VESSEL A MAJOR PORTION OF THE MAGNESIUM CHLORIDE REACTION BY-PRODUCT WHICH FORMS, EVACUATING SAID VESSEL AND HEATING IT TO BETWEEN 900* AND 1000*C. TO DISTILL OFF AND REMOVE RESIDUAL MAGNESIUM AND MAGNESIUM CHLORIDE, AND RECOVERING THE ADMITTING TITANIUM METAL PRODUCT.