Journal of Research of the National Bureau of Standards Vol. 55, No.5, November 1955 Research Paper 2628

Preparation of Titanium Tetrachloride of High Purity 1 w. Stanley Clabaugh, Robert T. Leslie, and Raleigh Gilchrist

A procedure is de cribed for the preparation of titaniulll tetrachloride of high purity. Procedures are also given for determining the purity of titaniulll tetrachloride by cryoscopic, spectrochemical, and infrared absorption measurements. The triple-point temperature of pure titanium tetrachloride was found to be 249.045° K, with an estimated uncertainty of ± O.OIQ o K.

1. Introduction 2 . Destruction of Organic Matter and Elim­ ination of Vanadium Titanium tetrachloride is generally produced by the reaction of chlorine with an intimate mixture of a It was found in this laboratory that organic titanium-bearing ore (or titanium compounds) and matter was removed from the titanium tetrachloride carbonaceous material. The titanium tetrachloride by addition of chlorine to the re£luxing tetrachloride. so produced will consequently contain as impurities The de truction of organic matter was accomplished volatile chlorides formed from sub tances occurring more rapidly if aluminum chloride hexahydrate and in both the titaniferous and the carbonaceous mate­ water were added as catalyst. It was found rials. Among the pos ible impurities will be chlo­ convenient and preferable to add the aluminum rides and oxychlorides of iron, vanadium, silicon, tin, chloride hexahydrate as a lurry, with an equal and carbon, especially carbonyl chloride and other amount of water. The total quantity of aluminum chlorinated organic compounds. chloride hexahydrate and water added wa about 2 The usual methods for refining the crude tetra­ percent of the mass of the titanium tetrachloride. chloride consist of a preliminary treatment of the A period of 2- to 6-hr re£luxing under th esc conditions liquid and a subsequent distillation. Among the was sufficient to eliminate the organic impurities. substances used for the preliminary treatment 2 are Sub sequent removal of the chlorine was accomplished sulfur, hydrogen sulfide,3 sulfuric acid, water, oleic by passing a tream of clean, dry ail' through the and stearic acids, metallic soaps, and a number of boiling tetrachloride, aILer which the tetrachloride metals, including copper. The particular functions was distilled. If the tetrachloride contained vana­ of most of these substances have not been made dium, the distilled product 'wa colored yellow. clear. Copper, however, appears to be very suitable The apparatu in which the tetrachloride was for removing vanadium. chemically treated consisted of a round-bottom 3- Experience with these methods, as well as with neek:ed Pyrex flask, a VigreLlx column of 45 em in variations of these methods, showed that none of heio-ht, a glass entrant tub e for the introduction of them consistently yidded high-purity titanium tetra­ chlorine, and a gJa s cap to close the thi.rd neck, chloride. Much depends on the previous history of through which material could be added to the flask. the so-called crude materials. In attempting to The Vigreux colu mn had an ou tlet to direct escaping prepare titanium tetrachloride in as high a "tate of vapors into the suction opening of the hood. purity as possible, for use in determining its funda­ The chlorine was dried by pas ing it through mental properties, it was found, by means of infrared concentrated sulfuric acid contained in a 250-ml spectroscopy, that organic material was the most gas-washing bottle, the entrant tube of ,,-hi.ch was persistent impurity. Emission spectroscopy showed equipped with a fritted end to disperse the chlorine. that all metallic impurities except vanadium and tin A safety valve, consisting of a second 250-ml gas­ were eliminated by a simple distillation of the tetra­ washing bottle nearly fliled with sulfuric acid but chloride. Vanadium was removed by treatment with not having a fritted entrant tube, was connected by copper and this element did not contaminate the means of a T-t ube between the first washing bottle tetrachloride. Tin was removed by means of a and the flask containing the tetrachloride. As an highly efficient still. added precautionary measure to prevent a,ccident, the entrant tube leading the chlorine inlo the tetra­ When it was realized that destruction and elimina­ chloride should be of a wide bore. tion of organic compounds in the tetrachloride was It was also found that organic matter can be the major problem, attention was concentratcd on destroyed by adding liquid bromine, equal to abou t this phase of the purification. one percent of the weight of the tetrachloride, and gently refluxing the resulting solution for several

1 Financial support of this work was furnished by the Metallurgy Branch of tbe hours. After excess bromine is removed bv a stream Office of aval Research, Department of the 'avy. of clean, dry air, the tetrachloride is distilled. The , P atents: British, 588,657; 600,003; 656,098; 674,315; German, 723,223; Swiss, 250,071; 255,404; 262,267; United States, 2,230,538; 2,289,327; 2,344,319; 2,370,525; distilled tetrachloride may have a yellow color, not 2,412,349; 2,416,191; 2,457,917; 2,463,396; 2,508,775; 2,512,807; 2,530,735; 2,533,021; 2,543,591; 2,555,361; 2,560,'123; 2,560,'124; 2,598,897: 2,598,898; 2,600,881. attributable to vanadium, because of the forma.tion 3 For use of hydrogen sulfIde see C. Kerby aud E. Pietz, Pilot Plant Distillation of a small quantity of titanium tetrabromic1e, or, and Purification of Titanium T etraebloride, U. S. Bur. Mines, Repts. Invest. No. 4153 (1947). more properly, of a bromo chloride. Trea tment with

261 aluminum chloride and chlorine will decompose in a reservoir and th e process of freezing, pumping, the bromo compound and cause the elimination of and melting was repeated four times. To remove the small amount of resulting bromine. products of hydrolysis th e tetrachloride was distilled To r emove the vanadium, the tetrachloride in a higb vacuum into the ampoules. The final previously freed from organic impurities was allowed product was found to have a purity of 99.999 mole to stand in contact with clean, greaseless copper percent. The tests for purity are described in the turnings. The copper became blackened by the following section. vanadium, and the tetrachloride became colorless. It was found that the vanadium was more efficiently 4. Examination for Purity removed if the organic matter was eliminated first. R efluxing the tetrachloride in contact with the cop­ Three independent physical methods were used to per hastened the deposition of the vanadium. establish the purity of the titanium tetrachloride pre­ The tetrachloride may be decanted from thl' pared by the foregoing methods of refining. copper and distilled, or distilled directly from th e copper. If the starting material contains unusually 4 .1. Cryoscopic Measurement of Purity large amounts of both organic matter and vanadium, To determine tbe degree of purity of the tetra­ the distill ed tetrachloride may have a slight yellow chloride, 50 ml of the purified compound was trans­ color or may turn yellowish on standing for several ferred by means of high-vacuum distillation to a days. A second treatment with aluminum chloride specially constructed iridioplatinum calorimeter. hexahydrate, water, and chlorine, however, will The material in the calorimeter was then frozen and complete th e destruction of any remaining organic gradually melted under equilibrium conditions. In matter. this method it is possible to determine only those impurities that are insoluble in the crystalline phase 3. Preparation of Titanium Tetrachloride of but soluble in the liquid phase. High Purity From the following observations by George '1'. Furukawa of the Thermodynamics Section of th e Al though the objective of the refining operations Heat and Power Division, the triple-point of th e pure was to produce titanium tetrachloride in as high a substance was calculated as well as the mole percent state of purity as possible, it was also of interest to of impurity in the tetrachloride. The observations ascertain the efficiency of simple chemical refining obtained on the purest product 4 are given in table l. as applied to crude tetrachloride of various origins. The plot of th e observed results yielded a slope of Experience sbowed that it was comparatively easy 0.00052. Using 0.019 as the cryoscopic constant to prepare titanium tetrachloride with a purity of (td-Im/RT2), calculated from the value of the heat of 99.99 percent, regardless of the souree of the starting fusion (!:1Hm= 12 .5 cal/g) as determined in the course material. As a matter of fact, it was less trouble­ of these experiments, th e mole fraction of solid in­ some to refine crude tetrachloride directly from the solu ble-liquid soluble impurity becomes 0.0000096, reaetor than it was to purify commercial tetra­ The mole percent purity then becomes 99 .9990. The chloride that had been partially refined before receip t. uncertainty of this figure is estimated to be ± 0.0002 Fifteen liters of titanium tetrachloride, obtained mole percent. on the open market, was purified by the procedure involving aluminum chloride h exahydrate, water, T ABLE 1. Results obtained for the purity of titanium tetra­ chlorine, distillation, and copper as outlined in sec­ chloride tion 2. Seven of the 15 liters so treated was further purified by careful fractional distillation in a Pod­ If F- I Observed ']'b bielniak still. The column of the still was packed of( with a heligrid fabricated from an alloy composed of 15.53 249.0369 6.32 249. 0418 5 percent of ru thenium and 95 percent of platinum. 3.53 249.0429 2.45 249. 0437 The heligrid occupied a space 1 in. in diameter and l. 73 249.0444 37 in. in length. The apparatus for distilling and l. 14 249. D444 1 e 249. 0445 collecting the various fractions was assembled by 0 e 249.0450 means of both tapered and spherical joints. Teflon gaskets were used in tbe joints to prevent leakage. Triple-point temperature, 249.045° K, with an estimated uncer· tainty of ± O.OLO° K.d During distillation the tetrachloride was protected Thermometer used, L 15. from the moisture of the outer atmosphere by guard 0° C ~2 73 . 1 6° K. tubes containing anhydrous magnesium perchlorate. The rate of return of liquid from the column to the a F is fraction melted. b The las.t two digits are significant only in the determination of small temper­ still pot was maintained at about 32 ml/min, by ature differences. e Extrapolated by moans of a lineal' equation fitted to the data by the method automatic control of the voltage to the heaters. A of least squares. reflux ratio of 70 to 1 was used. The distilling opera­ d 'rhe uncertainties given in this paper were estimated by examining the im­ precision of the measurements and all known sources of systematic error. 'rhe tion was completed in about 500 hr. The head frac­ system was ass umed to follow the ideal solution law and to fo rm no solid solution tion totaled 690 g, the middle fraction, 5,300 g, and with the impurities. th e residual fraction, 40 g. In the final purification • This was the material distributed to the con tractors participating in the Titanium Project administered by the Ollice of Naval Research, Department oC of the middle fraction the tetrachloride was placed the Navy, \Vashington 25, D ._C. 262 The purity of the pl'oducL obtained by simple To prepare such an aqueous solution, take eq ual ehemical refining, without subscq ucnt resort to the volumes of icc-cold titanium tetrachloridc and ice­ Podbielniak still, was calculated to be 99.992 mole cold water. It is immaterial whether the water is per cent. The uncertainty of this figure is estimated added to the Letrachloride or the tetrachloride to to be ± O.002 molc percent. the water. Add one to the other two drops at a time and allow the mixture to stand, between addi­ 4.2. Spectrochemical Measurement of Impurities tions, in an icc bath until fumes that form dissolve in the mixture. The one-to-one mixture is a thick, To dctermine impurities in the titanium tetrachlor­ syrupy yellow mass, which gradually becomes a ide by spectrochemical means, experiments were yellow transparent solution. On further dilution with made to ascertain the feasibility of diluting the tetra­ water, the solution may become slightly cloudy, but chloride with water, so that known quantities of this cloudiness disappears on standing. It should be certain elements could be added for control purposes. emphasized that the wholc forego in g operation must It was found that the tetrachloride could be slowly be conducted slowly. Concentrations of 4, 8, and diluted with water at the temperature of melting icc 12 g of elemental titanium in lOO-ml volumes were without hydrolytic precipitation of titanium. successfully prepared. These diluted solutions were remarkably stable. Such a solution, containing 8 T ABLE 2. L imits of detection of impurities in titanium tetra­ g of titanium in a volume of 100 ml, remained clear chloride by spectrochemical means for more than 4 months at room temperature. The spcctrochemical analyscs were performed by Limit or Limit of Element detee· cleLCe­ Martha Mayo Dan, of the Spectrochemistry Section Lion tion of the ChemisLl',Y Division . M easured amounts of the titanium solu tions were placed on graph i Le clec­ ppm ppm 0 Sil ve,·_.. __ ___ 0. 2 ~i(a gnes ium _------005 Ll'odes, and the elecLrodes dried at 105 C. The Aluminum I Man ganese __ _ _ .i Gold.______I electrodes wcr e then u cd as anodes in a ] 5-amp cl i rect Boron______. O. I Molybdenum. __ _ JO currenL arc. '1'0 determine the limiL of detec tion of B eryllium ___ .. _ . 02 N ickeL ______t Lead ______0.5 various foreign elements, known quantifies of the C,leium ______.05 Antimony _ 2 elemCll ts in tbe form of their salLs were added to the Columbium (niobium) __ <[0 Silico n ______0.5 CobaIL ______10 solution of the titanium teLrachlol'ide. The limiLs C hromium _ __ 1 T iIL ___ _ .2 Coppel'___ __ < 0. t T antalum __ 15 of detecLion of impurities in parLs pel' million of Vanadiulll __ 2 LiLanium tetrachloride arc given ill table 2. Iron . ___ _ .J "-rungs ten . __ 15 Gallium ___ _ .5 Zirconium __ _ 15 The results given in Labl e 3 were obtained on the H afnium __ 50 spectrochemical examin ation of (1 ) Lhe tcLrac]lloride of 99.9990 percent purity; (2) the teLracld oride of ' I' he limits of detection of clements n ot listed in t he table h ave not been establ ished. 99.992 percent puriLY; (3) a teLrachloricle lhaL was rrhc valtH's ~iven arc expressed in partsof Lhc metallic impurity in one m il­ lion parts of titanium tetraehloride. , chemically refined from starting material inlention­ ally conLaminaLed with silico n, iron, lead, mercury, TAR LE 3. Results of the spectrochemical examination of refined vanadium, copper, alumiuum, sulfur, and yarious titani1t?n tetrachloride organic subsLances such as carbonyl chloride, rLher, , acetic acid, and chloroace Lyl chlorides. The refinin g E lemen t 1 1H ateriai ,raterial ~\{ ateria l method used on material No. 3 was the same as that No.1 No.2 No. ;j used on material No.2, excepL thaL Lhe final product was not vacuum-distilled. ~i~~~~i~~;~':~ ~~::::::::::::-~:- :1 ~>- "b-;;;- - "g '~ - Boron ______0.2 0.2 0.2 4.3. Examination by Infrared Radiation B erylliulll . ______Infrared spectroscopy proved to be a valuable aid Caleium ______0.2 0. 1 0.2 Columbi.um (niobium) ______in detecting and determining those impmilies in Cobalt ______Chromiulll ______. ______titanium tetrachloride not readil y or ca s il~' deter­ Coppel' ______0. 2 0. 2 0. 2 mined by other means. A detailed discussion of Iron ______< 0.5 this work has been given.5 Some of the substances Gallium ______. ______._ H afnium ______------I determinable by infrared absorption spectroscopy M agnesllIlll ______< 0. I < O.l < 0. 1 are listed in table 4. ~if a n ga n c se ______Ko effort was made to ascertain the limits of M olybdenum ______N ickel ______.. ______detection for carbon dioxide or hydrolysis product, Lead ______because both of these sub tances can be eliminated AnLimony __ _ _ --- ____ _ Si lico n ______0.5 0.5 by a single careful distillaLion in an inert atmosphere rpin ______or in a high vacuum. 'Whereas the sensitivity is rpantalulIl . . ______.. 110t Vanadiu lll ______. __ good for either vanadium oxytrichloride or silicon rpungstcn _____ . __ tetrachloride, vanadium and silicon can be deter· Zirco nium ______mined by other meUlods. Vanadium oxytrichloride

NO'!' I'; : <, means less t han ; , means not detected ; - ?, ' R . B. Joha nnesen , C. L. Gorcl on, J . E. Stewart, and R . Gilchrisl, J. Hesearch means detection doubtful. N B S 53, J97 (1954 ) R P2533. 263 TABL E 4. Charactel'istic infraud absorption peaks and limits produces a visible yellow color in low concentrations, of detection of common impurities in titanium tetrachloTide and 1 ppm can be detected spectrophotometrically at 390 millimicrons if a 10-mm cell is used. As Wavelength Limit of Impurity of peak detection shown in table 2, silicon can be detected by spectro· chemical means in a concentration as low as 0.5 ppm.

Po ppm Infrared examination revealed that material No. 1 H ydrogen chloride, H CJ ______3.53 2 Carbon dioxide, CO, ______4. 30 ? contained about 1 part of trichloroacetyl chloride Vanadium oxytrichloride, VO Cl, ______4.84 40 in one million parts of the titanium tetracloride, Carbon yl chloride, COCJ, ______5. 51 ca. 2 Chloroacetyl chloride, CICH,COCL ______5. 55 0.5 material No.2, 8 parts, and material No. 3, between Dichloroacetyl chloride, ChCH COCL ______5. 55 1 2 and 3 parts. Trichloroacetyl chloride... Cl,CCOCL ______5. 55 0. 5 Silicon tetrachloride, Si LO I, ______8. 14 200 H ydrolysis'product. ______8. 45 ? WASHINGTON, July 22, 1955.

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