Determination of Titanium, Zirconium, Niobium, and Tantalum in Steels: Separations by Anion-Exchange John 1

Home , Ammonium fluoride, Ammonium nitrate, Ammonium oxalate, Ammonium phosphate

Journal of Research of the National Bureau of Standards Vo!' 62, No.1, January 1959 Research Paper 2923 Determination of Titanium, Zirconium, Niobium, and Tantalum in Steels: Separations by Anion-Exchange John 1. Hague and Lawrence A . Machlan A procedlll'e is described for the determination of titanium, zirconium niobium and tantalum in steel. These elements are concentrated by selective precipita'tion with' cup ferr on from a hydrochloric acid solution of the sample, and t hen ignited to t he oxides. The oXides are fused, and dissolved in a hydrochloric-hydrofluoric acid m ixtlll'e. Three sepa rate eluates, containing titanium and zirconium, niobium, and tantalum result from elu tion with mixtures containing ammonium chloride, hydrochloric acid, and hydrofluoric acid from a column of Dowex-l anion-exchange resin. Boric acid is added to the clu ates to complex t he hydrofluoric acid, and the elements are precipitated wit h cupferron. Titanium is deter mmed by the hydrogen-peroxide method, and zirconium by the phosphate-gravimetric method. NIOblllm and tantalum are determl11ed by the hydroquinone- and pyrogallol photometflC methods, or by welghl11g the oX ides. 1. Introduction A concentration of Litanium, zil'co llinum, Iliobiulll, and tantalum is eff ected by cupfeJ'l'oLl prcci pitation T he incrcase d usC' in recent years of clements [4, 5] with most of the iron present in the reduced t hat form complexes with carbo;, and nitroO'en in co ndition. The small amount of iron coprecipit ated metallurgical alloys has presented some inte;esti ll g serves as a gathering agent. Most of the chromium, probl~ms to the analytical chemist. For example, nickel, cobalt, manganese, and iron pass into the ~he hIgh-temperature and heat-resisti ng alloys used filtrate, so that a satisfactory cO ll centration can often J': rockets and jet engin es contain variou s combi na be made from a sample as large as 25 g. tIOns of tungsten, molybdenum, titanium zirco , The e upfel'l'on precipitatc is ignited to the oxide, nium, niobium, tantalum, and aluminum in ~dd i Lion leached with hydrochloric acid, and filtered . The to t h~ major elemenls, nickel, cobal t, iron , alld filtrate is evaporated nearly to d1'.fness, The in chrommm. Even t he usual grades of stabilized soluble material is ignited, treated wiLh sulfuric and stainless steels are becoming complex alloys throuo'h hydrofluoric acids to eliminate sili ca, and fused in the use of scrap in melting charges. Becausc bof sodium pyrosulfate. A mixture containing 50 per the c ompl ex i t ~ · of these materials, spectrographic ce nt by volume of hydrochloric acid and 10 perce nt alld X-ray methods are desirable for production by volume of hydrofluoric acid is added to Lhe con trol and acceptance testing. Adequate chemical evaporated filtrate, and the melt is dissolved in the procedures for the analysis of stand ards used in resulting solu tion . cay~rati!lg the~e instruments ~re esp eC.i ally . nee~ed . The solution is transfer.l'ed to an a nion-exchange 1 he dIfficultws encountered m handlIng combma column, and the t itanium and zir('o niu mare elu ted tions of zirconium, titanium, niobium, and tanta with a 50-percent hydrochloric 10-percell t hydro lum ar:e well known [10 , 19].1 During the last few fluoric acid solution. A second fraction COil taini ng ~- cars It bas been shown [1, 20] that combinations molybdenum, tin, and iron is eluted with a mixture of titanium, niobium, and tantalu m can be separated containing 12.5 percent by volume of hydl'odJoric by selective elution from cellulose columns with acid, 20 percent by volume of hydrofluoric acid find methyl ethyl ketone in cO,mbination with hydro 7.2 percent by weight of ammonium chloridC' , find fluonc and hydrochlol'lc aCIds or t heir ammonium discarded. Niobium is collecLed ill a third fraction salts. Several papers [2, 6, 14, 15, 16] have shown by elution with an ammonium chl oride-hydrofluoric that useful separations in this group of elements acid solution. Tantalum is collected in a fourth Ca!l be made on anion-exchange resin columns, using fraction by elu tion with an ammonium chlol'ide mIxtures of hydrochloric and hvdrofluoric acids as ammonium fluoride olution adjusted to a pH of elu tion reagents. " 5 to 6. The method described here provides for the deter The first fraction containing the titanium and mination of titanium, zirconium niobium and zirconium (and in addition, such elements as chro tantalu m in the range of a few th~usandths bf one mium, nickel, tungsten, and vanadium) is mixed perce nt to approximately one-half perce nt in steels. with a boric acid solution to complex the hydro The procedure involves most of the separations re fluQI'ic acid. A small amount of iron is added as a quired in determining larger percen tages of these gatherer, and a precipitation is made with cupferron. clements and illustrates the application of the ion The precipitate is ignited , fused in pyrosulfate and e,xchange ~echnique to otherwise very difficult separa dissolved in hydrochloric acid. A so dium hydroxide tlO J1S. Drrect photometric methods for the deter precipitation [10, p . 579] is made to eliminate vana mina,tion of molybdenum [10, p. 315] and tungsten dium and tungsten, and the precipitate is ignited. [18] lJl steels are available for this concentration The oxide mixture is fused in pYl'osulfatc and dis range, an~ these elements ~re !lot co nsidered except solved in diluted sulfuric acid. Titanium is deter as they affect other determmatIOns. mined in a suitable aliquot by a differential photo

I Figures in brackets ind icate the literature refcrCll C€S at the ene! of this paper, metric measurement of the colored complex formed

11 with hydrogen peroxide [10 , p. 581]. The solutions necessary are made of Tygon R tubing. The flow used for the photometric determination of titanium of solu tions is controlled by hosecock clamps on the are combined, and zirconium is determined by the flexible connections. The connections should be phosphate method [10, p. 569]. carefully done and checked to avoid any possibility The third fraction containing the niobium is of leakage of the solutions containing hydrofluoric treated with boric acid to complex the hydrofluoric acid. acid, and zirconium, low in niobium and titanium, Resins. Dowex-1 , 200- to 400-mesh, 8- to 10- is added as a coprecipitant. After precipitation percent divinylbenzene cross linkage are used. with cupferron, the ignited oxide is fused in pyro Experience over a period of several years has shown sulfate and dissolved in ammonium oxalate solution. that the mesh size of these resins may vary consider A suitable aliquot of the solution is evaporated to ably from lot to lot. In order to avoid difficulty, fumes with sulfuri c and nitric acids to destroy the the resins as received are air dried, and sieved through oxalate ion. The niobium is determined photo a 270-mesh sieve. Material retained on the 270- metrically with hydro quinone [11, 12] in concen mesh sieve is used for other purposes. Most of the trated sulfuric acid. Larger amounts of niobium, fines are removed from the fraction passing the 270- such as are encountered in type 347 stainless steel, mesh sieve as follows: Prepare a suspension of the can be precipitated with cupferron after the addi resin in diluted hydrochloric acid (1 + 19). This tion of boric acid, ignited to the oxide, and weighed. terminology denotes 1 volume of concentrated Tantalum in the fourth fraction is recovered from hydrochloric acid, sp gr 1.18, diluted with 19 volumes the eluate by precipitation with cupferron after the of water. If no dilution is specified, the concentrated addition of boric acid and zirconium. The ignited analytical reagent is meant. The coarser fraction is oxide is fused in pyrosulfate and dissolved in am allowed to settle 10 to 15 min, and the fines removed monium oxalate-ammonium citrate solution. The by decantation. Repeat the process several times photometric determination of tantalum employs the until most of the very fine material has been re color reaction with pyrogallol [10, p. 610] . Larger moved from the suspension. amounts of tantalum can be precipitated with cup Cover the bottom of the ion-exchange column with ferron after the addition of boric acid, ignited to the a layer of acid-resistant vinyl-chloride plastic wool, oxide and weighed. X- to %-in. thick. Add portions of the resin sus The present procedure is somewhat long, as two pension to obtain a settled column of the resin 6 to 7 days are required to carry out the ion-exchange in. high. The loaded column should be run through separations, unless the columns are operated con several cycles of elution with alternate additions of tinuously, and several days are required to finish the diluted hydrochloric acid (3 + 1) and diluted hydro various determinations. The method does, however, chloric acid (1 + 9) to remove the remainder of the compare favorably in time and ease of operation fines. The column is then washed with diluted with the other chemical methods available for this hydrochloric aeid (I + 3) and is ready for use. comb~nation of elemen ts, and lends itself readily to Resin columns prepared in this way have been used handhng a number of samples at the same time if for several years. The only maintenance required enough columns are prepared. is to empty and refill the column with the resin charge if the flow rate becomes excessively slow due 2. Apparatus and Resins to packing. The resin charge should not be allowed Ion-Exchange Columns. The columns are con to become dry. structed of polystyrene and are approximately 12 in. Polyethylene Ware. 250-ml and 600-ml Griffin long and of 1 in. inside diameter. A simple column form beakers are required. The high-temperature can be prepared from a 12-in. length of polystyrene polyethylene ware is useful for evaporations at tubing as follows: The bottom of the tube is closed steam-bath temperatures. Bottles are used for by a waxed No.5 rubber stopper with a YIs-in. hole. preparing and dispensing acid mixtures containing hydrofluoric acid. A 6-in. length of polystyrene tubing, ~{ s in. outside diameter, Hs-in. bore, is inserted into the hole flush Colorimeter. An Evelyn type of colorimeter, with the upper surface of the stopper. Another including filters, voltage stabilizer, and galvanometer, 6-in. length of this tubing is attached to the smaller was used for the measurements reported. Matched tube with a 2-in. length of Tygon R tubing, and the test tubes (22 by 175 mm) were used as absorption flow controlled by a hosecock clamp on the Tygon cells. tubing. However, if a number of analyses are to be 3. Procedures and Discussion made, it is convenient to arrange the colmIDls so that a number can be operated with a minimum of 3.1. Preparation of the Solution for Ion-Exchange attention, as has been done previously with glass Separations columns [7]. Plastic columns suitable for such an assembly have been developed [13J . The columns Reagents used in this work were obtained and assembled as Cupferron Solution (60 g/liler). Dissolve 6 g of illustrated in figure 1. cup ferron in 90 ml of water, dilute to 100 ml, and These columns are equipped with machined "Dole filter through a dry filter. This solution should be type" fittings of polystyrene. Inlet and outlet tubes prepared as needed and cooled (5° C), as the solution are of polyethylene; flexible connections where is not stable.

12 FIGURE 1. A ssembly (left) and close-up view (right) of ion-exchange columns. Oupjerron Wash Solution. Add 25 ml of cupferron settle. Filter through a double 7- cm close-textm e solutIOn to 975 ml of cold (5 ° C) diluted hydro fil.ter paper fitted Lo a Buchner fLmn el and precoated chloric acid (1 + 9). Prcpare as needed. WIth some fil ter pulp. Transfer the precipitate to the iWlIlel .and wash well, using 400 ml of cupferron Procedure wash solutIOn. T~·an s fer. the precipitate and papers Transfer 5 to 25 g of the sample to a covered 600- to a 30-ml porcelam crucible, and carefully ignite at or 800-ml beaker, and add 225 to 450 ml of diluted a low temperature (500° to 550° C) until carbon is hydrochloric acid (J + 2). Warm the solution on a removed. steam bath, or if necessary over a burner until the Transfer m.ost of the ignited oxides to a 250-ml sample dissolves. Adjust the volume of the solution beaker, and dissolve the remainder in the crucible in with water to 400 to 500 ml, so that the solution wa~"lll diluted hydrochloric acid (1 + 1). Finally contains approximately 15 percent by volume of pohce and wash the crucible, with the same acid transferring the washings to thc 250-ml beaker: hydroc~110ric acid. (One gram of iron requires approxll11ately 3 ml of hydrochloric acid for solution.) Adjust the volume to about 30 to 35 ml with diluted Cool the solution to 5° C, and add cup ferron solu hydrochoric acid (1 + 1), and digest on the stearn bath for several .1lOurS. Add paper pulp, and filter •Lion chop wise and• with. continuous stirrinO"b until the Iron starts to preClpltate. The precipitate will beO"in the warm s.ol.utlOn thl"ough a 9-cm close-textm e Lo coagulate when precipitation of titanium :ir paper contammg pulp, catching the filtrate in a conium, niobium, tant~l~~ , vanadium, etc., is 'com 250-ml high-temp erature polyethylene beaker . plete. Add several millilIters of cup ferron in excess Transfer the lmdissolved residue to the paper and wash with diluted hydroc.hloric acid (1 + 1). Evapo (approximately 25 to 30 ml in total), which will cause rate the filtrate and washmgs to a volume of approxi the precipitate to assume a reddish color. The pre mately 5-ml, and reserve . . Transfer the precipitate cipitated iron will act as a "gatherer" for the other and paper to a 25-ml platmum crucible, and ignite elements. Add a ball of paper pulp equivalent to at a low temperature. about one-half of an ll-cm filter paper, stir until the A~d 1 ~l of sulfmic a?id and 10 to 15 ml of hydro pulp is well dispersed, and a11O"1v the precipitate to fluonc aCld to the crucIble, and remove the hydro-

13 fluoric and sulfmic acids by heating on an air or solution is referred to as 14- 4 acid mixture in the sand bath, being careful that the sulfuric acid does procedure. not creep over the top of the crucible. Finally ignite Ammonium Ohloride-Ammonium Fluoride Solution. at a low temperature, and fuse the oxides with 1 g of Transfer 600 ml of ammonium chloride solution and sodium pyrosulfate. 40 ml of hydroHuoric acid to a polyethylene beaker. Add 30 ml of a hydrochloric-hydrofluoric acid Adjust the solution to a pH of 5 to 6 with ammonium mixture, containing 50 percent by volume of hydro hydroxide (approximately 80 to 85 ml will be re chloric acid and 10 percent by volume of hydro quired), and dilute to 1 liter with water. This fluoric acid, to the polyethylene beaker. Transfer solution must be prepared with reasonable care, as the crucible and melt to the beaker, and warm on a a solution which is too acid will not completely elute steam bath. Manipulate the crucible with a poly the tantalum in the volume specified in the procedure. ethylene stirring rod until the melt dissolves, remove A solution which is too alkaline will precipitate the crucible with the rod or platinum-tipped tongs, tantalum in the column, spoiling the determination and wash well with the 50-percent hydrochlorlc- and the one which follows. This solution is referred 10-percent hydrofluoric acid solution. The solution to as 14- 4 neutral mixture in the procedure. should be clear for the separations which follow to P.rocedure succeed, and the volume should be approximately 50 to 75 ml. Transfer 50 ml of the 50- 10 mixture to the column If large quantities (25 mg or more) of titanium or in small increments (5 to 10 ml), and drain the acid zirconium are present, the amount of flux and the to 1 cm above the resin bed. Discard the eluate. volume may have to be increased to obtain a clear Transfer the solution, prepared according to the solution. Alternatively, the solution may be filtered directions in the previous section, in small increments through a close-texture paper onto the column, and (5 to 10 ml) to the column with the bottom hose-cock the paper washed thoroughly with the hydrochloric clamp open. Add the sample as the solution moves hydrofluoric acid solution to dissolve any insoluble down the column until all the sample has been material. transferred. Wash the beaker 4 to 5 times with The fusion is made with sodium pyrosulfate be 5-ml portions of the 50- 10 mixture, and finally wash cause the potassium salt forms insoluble fluoroborates down the sides of the column several times with the in the procedure described in section 3.3.a. If same mixture. Discard the first 20 or 25 ml of titani Lim and zirconium determinations are not de solution from the column, and collect the remainder sired the fusion may be made with potassium pyro of the first fraction, containing the titanium and sulfate, provided the tantalum does not exceed 50 mg zirconium (+ hafnium) along with vanadium, tung or so; otherwise sparingly soluble potassium fluoro sten, chromium, etc., in a 600-ml polyethylene tantalate will precipitate. Such solubility considera beaker. Add a total of 350 ml of the 50- 10 mixture, tions do not arise with mixtures of hydrous oxides this volume to include the washings and the solution or metals, which can be dissolved directly in the used to elute the fraction. The hose-cock clamp mixed acids. should be adjusted so that the flow of the solution is approximately 100 to 125 ml/hr. Allow the solu 3.2. Ion-Exchange Separation of Titanium and tion to drain to the top of the resin, and wash down Zirconium (+ Hafnium), Niobium, and Tantalum the sides of the column with six or seven 5-ml portions (a total of about 35 ml) of the 7- 12 ~-20 mixture, Reagents allowing the solution to drain to the top of the Hydrochloric-Hydrofluoric Acid Solution. Add 500 column each time. Reserve the beaker containing ml of hydrochloric acid to 300 ml of water, add 100 the first eluate, and replace it with another 600-ml ml of hydrofluoric acid, dilu te to 1 liter with water, polyethylene beaker. and mix well. The solution is referred to as 50- 10 Add a total of 350 ml of the 7- 12 ~-20 mixture at mixture in the procedure. a How-rate of approximately 100 to 125 ml per hour, Ammonium Ohloride Solution (240 g/liter). Dis and allow the solution to drain to the top of the solve 240 g of ammonium chloride in 800 ml of column. Wash the sides of the column with six or water by warming, and dilute to 1 liter with water. seven 5-ml portions of the 14- 4 acid solution, remove Filter to remove insoluble material. This solution the beaker containing the second fraction, and is used as a stock solution in preparing the three replace with another 600-ml polyethylene beaker. solutions which follow. The second fraction contains primarily iron, and Ammonium Ohloride-Hydro c hl 0 ric-Hydrofluoric molybdenum and tin if present, and can be discarded. Acid Solution. Transfer 300 ml of ammonium Add a total of 300 ml of the 14- 4 acid mixture, chloride solution, 200 ml of hydrofluoric acid and 125 maintaining the technique and How-rate described ml of hydrochloric acid to a polyethylene bottle. in the previous paragraph. Wash the sides of the Dilute to 1 liter with water, and mix well. This column with approximately 25 to 30 ml of the 14- 4 solution is referred to as 7- 12 ~-20 mixture in the neutral mixture, remove the beaker containing the procedure. third fraction (niobium) and reserve. Replace the Ammonium Ohloride-Hydrofluoric Acid Solution. beaker with a 600-ml polyethylene beaker. Transfer 600 ml of ammonium chloride solution and Elute the fourth and final fraction by the addition 40 ml of hydrofluoric acid to a polyethylene bottle, of a total of 300 ml of the 14- 4 neutral mixture, and dilute to 1 liter with water, and mix well. This reserve the solution for the determination of tanta- 14 lum. The column is cleaned by the addition, in 30 ml of dilu ted hydrochloric acid (1 + 9). R emove increments, of 50 ml of diluted hydrochloric acid the crucible, and wash with warm water. (1 + 3), after which it is ready for the next sample. Add sodium hydroxide solution until the solution It should b e mentioned that painful burns can is neutral to litmus paper, then add an excess of result from careless handling of hydrofluoric acid 5 ml and heat to boiling. Boil for 5 min, add a olutions. Any spills should be promptly washed small amount of paper pulp, and fil ter the warm up, and borax, or similar proprietary compounds, solution through a close-texture paper containing hould be used several times a day in washing the pulp. Transfer the precipitate to the paper, and bands or any skin area exposed to hydrofluoric acid. wash 12 to 15 times with ammonium nitrate (20 gfliter) wash solution. Transfer the paper and 3.3. Determination of Titanium, Zirconium (+ Haf precipitate to a pOTCclain cru cible, and ignite at a nium), Niobium, and Tantalum low temperature. F'use the ignited oxides in 1 & of potassium pyrosulfate, dissolve t he melt in 30 ml of a . Titanium diluted sulfuric acid (1 + 9), and add a little paper pulp. Filter the solution through a close-texture Reagents paper containing paper pulp, catcbing the filtrate in a lOO-ml volumetric flask. Wash 8 Lo 10 times, Ferric Sulfate Solution (50 g/liter ). Dissolve 5 g of and dilute to volume, with diluted sulfuric acid hydrated ferric sulfate (low in titanium and zirco (1 + 9). If necessary, transfer a suitable aliquot nium) in 90 ml of diluted sulfuric acid (1 + 9); and containing not more than 2.5 mg of titanium to a dilute to 100 ml with diluted sulfuric acid (1 + 9). lOO-ml volumetric fl ask and diluLe to the mark with Sodium Hydroxide SoLution (100 g/liter). Dissolve dilu ted sulfuric acicL (l + 9). Since the solu tions arc 10 g of sodium hydroxide in 80 ml of water, and to be combined for the determination of zirconium, all dilute to 100 mL aliquoLing, cell rinsing, etc., should be carried ouL in Ammonium Nitrate Wash Solution (20 gfliter). such a way as to achieve this objective. Dissolve 10 g of ammonium nitraLe in 400 ml of For the photometric deLermination of Litanium, water, and dilute to 500 mL rinse a photometer cell 3 times with 3 to 4 ml of the Standard Titanium Sulfate Solution (1 mloO .25 solu tion from the lOO-ml volumetric flask, Lrans mg oj titanium). Transfer 0.4170 g of titanium felTing the rinsings to a 400-ml beaker. Transfer dioxide (a suitable portion of NBS Standard Sample 15 ml of the solution to a 2-cm photometer cell for 154a may be used) to a 250-ml Erlenmeyer flask, add use as a reference solution. Add 1.0 ml of hydrogen 10 g of ammonium sulfa,te and 25 ml of sulfuric acid , pOl'oxide (30 %) to the solu tion remainin~ in the flask insert a short-stemmed glass funnel in the !l eck of and mix Lhoroughl~' . Transfer a suiLable portion to t he flask and heat cau tiousl:v to incipien t boiling the maLched 2-cm photomeLer cell for usc as the while rotating t he flask over a free flame. Continue sample solution . Using Lhe reference solution, adjust the heating until complete solution has been effected the photometer to the iniLi al seLting using a na,rrow and no unattacked material remains on the wall of light band ce nLered at approximately 410 mIL. the flask. Cool and rapidly pour the solution into vVhile maintaining this phoLomeLer adju tment, take 450 ml of cool water which is vigorously stirred. Lhe photometric reading of the sample solution. Rinse the flask with diluted sulfuric acid (5 + 95 ). Transfer the solutions to the 400-ml beaker, and Transfer the soluLion Lo a l,OOO-ml volumetric fl as ].,;: , reserve for the dctermination of zirconium, Deter dilute to the marl;: with diluted sulfuric acid (5 + 95 ), mine the amount of titanium from a calibration curve and mix thoroughly. prepared as follows: Transfer 0.0, 2.0, 5.0, and 10.0 Procedure ml of standard titanium soluLion to each of four] 00- ml volumetric flasks, and dilute to volume with Transfer 40 g of boric acid to a 1,500-ml beaker, diluted sulfuric acicL (1 + 9). Continu e as described add 700 ml of water, and warm to dissolve the acid. in the preceding paragraph, and plot the photometric Add the first fraction of solution containing the readings of the calibration solutions with respect to titanium and zirconium to the warm boric acid milligrams of titanium, or calculate a factor [8]. The solution with continuous stirring, and add by pipet solutions obey Beer's Law and blanks are usually 2 ml of the ferric sulfate solution. Cool to 5° C, negligible. Since "difference" photometric measure and add 25 to 30 ml of cupferron solution slowly ments of this type are dependent for accuracy on an while stirring. Add paper pulp, stir the solution additive absorbancy Jun ction, a narrow-band filter well to distribute the pulp, and allow the precipitate photometer or spectl'Ophotometer is desirable for to settle for 10 to 15 min. Filter through a double the measurements. thickness of close-texture filter paper fitted to a 7-cm Jn preparing the solution for the sodium hydroxide Buchner funnel and precoated with a little filter pulp. separation, a turbid solution is obtained if the sample Transfer the precipitate to the funnel, and wash well contains appreciable tungsten. The sodium hy with 400 ml of cold (5 ° C) cup ferron wash solution. droxide separation removes most of the tungsten, Transfer the paper and precipitate to a 25-ml por along with the vanadium. In order to check for the celain crucible, and ignite at a low temperature until complete removal of vanadium, photometric read the carbon has burned. Fuse the ignited oxides in ings on the peroxide treated solution were made at 1 to 2 g of potassium pyrosulfate, transfer the cru approximately 515 mIL. A change in ratio of the cible to a 250-ml beaker, and dissolve the melt with absol'bancy at 410 m.u to that at 515 mIL will indicate 15 vanadium. Vanadium occlusion in the precipitate 40 g of ammonium oxalate in 900 ml of warm water, amounts to less than the equivalent of 0.1 mg of filter if necessary, and dilute to 1,000 ml with water. titanium, even where as much as 50 mg of vanadium Stannous Ohloride Solution (200 g/liter). Dissolve is involved. 100 g of stannous chloride dihydrate in 400 ml of b . Zirconium (+ Hafnium) diluted hydrochloric acid (1 + 1) by heating on the steam bath. Cool and dilute to 500 ml with diluted Reagents hydrochloric acid (1 + 1). Ammonium Phosphate Solution (300 g/liter). Dis Hydroquinone Solution (50 g/liter). Dissolve 20 g solve 60 g of diammonium hydTogen phosphate in of hydroquinone in 400 ml of sulfuric acid. 150 ml of water. Filter if necessary, and dilute to Standard Niobium Solution (1 mZo40 jJ-g oj ni 200 ml with water. obium). Transfer 0.0115 g of niobium pentoxide to Ammonium Nitrate Wash Solution (50 gfliter). a porcelain crucible. Add 1 g of potassium pyro Dissolve 25 g of ammonium nitrate in 400 ml of sulfate, heat to fuse the niobium oxide, and dissolve water, and dilute to 500 ml with water. the cooled melt with continuous stirring in 30 ml of warm ammonium oxalate solution. Transfer the Procedure cooled solution to a 200-ml volumetric flask and Transfer all of the sample solution and washings dilute to volume with ammonium oxalate solution. from the titanium determination to a 400-ml beaker, This solution shoulcl bp, prepared as needed. and adjust to a volume of 200 ml or less, with the Procedure acidity approximately 10 percent by volume. in To the third fraction (approximately 300 ml) sulfuric acid. Add 1 to 2 ml of hydrogen peroxlde containing the niobium, add 15 g of boric acid, 70 (30 %) and 25 ml of ammonium phosphate solution, ml of hydrochloric acid, 80 ml of water, and 2 ml of and allow to stand overnight at a temperature of zirconium sulfate solution. Warm on the steam 35° to 40° C. (with a milligram or less of zirconium, bath (30° to 35 ° C) and stir occasionally to dissolve let the solution stand a day or two). Add 1 ml of the boric acid. Cool to 5° C, and add slowly while hydrogen peroxide, cool, add paper pulp, and filter stirring, 30 ml of cupferron solution. Add paper through a close-textme paper containing a little pulp. pulp, stir well to distribute the pulp and allow to Transfer the precipitate to the paper, and wash stand 10 to 15 min. Filter through a double thick 18 to 20 times with ammonium-nitrate wash solution ness of 7-cm close-texture paper fitted to a Buchner (50 g/liter). Unfortunately, the zirconium ph~s funnel. Transfer the precipitate to the filter, and phate precipitate tends to change composition, so the wash well using 400 ml of cold cupferron wash solu washing technique should be such as to leave the tion. Transfer the paper and precipitate to a porce proper composition [10,p. 569. footnote 20] . Transfer lain crucible and ignite at a low temperature (500° the paper and precipitate to a weighed porcelain to 550° C). Add 1 g of potassium pyrosulfate to crucible, and ignite first at a low temperature to the crucible, and fuse to dissolve the mixed oxides. remove carbon, and finally ignite at 1,050 0 C. for Transfer the crucible and melt to a 100-ml beaker 20 min. Cool, and weigh as ZrP207 + HfP20 7' and dissolve the melt in 25 ml of warm ammonium The precipitate also contains any hafnium in the oxalate solution. The fusion should be agitated alloy, since the acid mixture chosen for elution does with a stirring rod while dissolving, in order to pre not give an appreciable fractionation of titanium, vent a localized high concentration of niobium zirconium, and hafnium. If suitable conditions can which might lead to the precipitation of the hydrous be established without too much extra manipulation, oxide. Transfer the solution to a 100- or 200-ml the use of mandelic acid [9,17] as a precipitant is volumetric flask, and dilute to volume with am attractive, particularly for the larger amounts where monium oxalate solution. Transfer a suitable ali the advantage of the phosphate conversion factor is quot containing not more than 0.3 mg of niobium to more than outweighed by the lack of a definite com a weighed 100-ml beaker. position. A good color reaction reasonably specific Add 10 ml of diluted sulfuric acid (1 + 1) , 5 ml of for zirconium is also needed for small quantities, nitric acid, and 3 to 5 ml of hydrochloric acid. Heat where the normal hafnium ratio of 2 or 3 percent on a hot plate until moderate fumes of sulfuric acid is no t cri ti cal. are evolved, cool, and wash down the sides of the c. Niobium beaker with water. Cool, add 2 or 3 drops of hydro

Reagents gen peroxide (30%), and again heat to moderate fumes of sulfuric acid. Repeat the washing and Zirconium Su(fate Solution (1 mloapproximately hydrogen peroxide addition, and again evaporate to 10 mg oj zirconium). Dissolve 3.90 g of zirconium fumes. Finally, wash down the sides of the beaker, sulfate tetrahydrate in 75 ml of diluted sulfuric acid and heat to moderate fumes of sulfuric acid. Cool, 0 + 19), transfer to a 100-ml volumetric flask, and add 1 drop of stannous chloride solu tion, and mix dilute to volume with diluted sulfuric acid 0 + 19). well by swirling the beaker. Add hydroquinone This solution must be low in titanium and iron, as solution to make 100 g of solution in the beaker, and well as niobium and tantalum. It was prepared mix the solu tion thoroughly. Transfer a suitable from salt purified by the method of Clabaugh and portion of hydroquinone solution to a 2-cm photom Gilchrist [3]. eter cell for 'use as a reference solution. Transfer a Ammonium Oxalate Solution (40 g/liter ). Dissolve portion of the test solution prepared above to a 16 matched 2-cm photometer cell for use as the sample tantalum). Transfer 0.0305 g of tantalum pentoxide soluLion. Using the reference solution, adjust tne to a porcelain crucible. Add 1 g of potassium photometer to the initial setting using a light band pyrosulfate to the crucible, heat to fuse the oxide, centered at 490 mi!. While maintaining this pho and dissolve the cooled melt with continuous stirring tometer adjustment, take the photometric reading in 75 ml of warm ammonium oxalate-ammonium of the sample solution. citrate solution . Transfer t he cooled solution to a Determine the amount of niobium present in the 200-ml volumetric flask and dilute to volume with test solution from a calibration curve prepared as ammonium oxalate-ammonium citrate solution. This follows: Transfer 0.0, 2.0, 5.0, and 10.0 ml of stand solution should be prepared as needed. ard niobium solution (40 ,ug;ml) to four wPighed Procedure 100-ml beakers, and continue as directed in the pre ceding paragraph. Plot the photometric readings To the fourth fraction (approximately 270 ml), of the calibration solutions with respect to micro containing t he tantalum, add 8 g of boric acid, 75 grams of niobium. The hydro quinone photometric ml of hydrochloric acid, 80 ml of water, and 2 ml of zirconium sulfate solution. Warm on the steam method has an appreciable temperature coefficient 0 0 (approximately 0.6 to 0.7 % /deg) , 80 that the pho bath (30 to 35 C) and stir occasionally to dissolve tometric readings must be carried out at a con the boric acid. Cool to 50 C and add slowly, with trolled temperature, or a separate set of calibration continuous stirring, 25 ml of cllpferron solution . solutions must be carried along with each set of Add paper pulp, stir well to distribute the pulp determinations. Since it was not convenient to and allow the solution to stand 10 to 15 control the temperature, the latter alternative was min. Filter through a double tllickness of used for the determinations reported in this paper. 7-cm close-texture paper fitted to a Buchner funnel. The photometric measurements on these solutions Transfer the precipitate to the filter, and wash vlcll follow Beer's Law, and blanks are usually negligible. with 400 ml of cupferron wash solution. Transfer The wavelength selected for the measuremen ts is on the paper and precipitate to a porcelain crucible, and ignite at a low temperature (500 0 to 550 0 C). i he long wavelength side of the peak absorbancy primarily to extend the concentration range, and Add 1 g of potassium pyrosulfate to t he crucible, because somewhat. better precision was obtained. and fuse to dissolve the mixed oxides. Transfer the It is more convenient to determine niobium in a crucible and melt to a 100-ml beaker, and dissolve suitable aliquot by developing a color with hydrogen the melt in 25 to 50 ml of warm ammonium oxalatc peroxide [21J in a sulfuric-phosphoric acid medium, ammonium citrate solu tion. The fusion should be but the zirconium used as a gatherer interferes in agitated with a stirring rod while dissolving, in order this procedure. Attempts to use tin as a gatherer to prevent a locali zed high concentration of tantalum were not successful because the ignited oxides do which might lead to t he precipitation of the hydrous not fuse readily in pyrosuHate. If 20 mg or more of oxide. Transfer t he solution to a 50- or 100-ml niobium is involved, the determination can be con volumetric :flask and dilute to volume with am veniently completed by precipitation with cupferron monium oxalate-ammonium citrate solution. Trans as described in t he first paragraph of this procedure. fer with a pipet 25 ml of pyrogallic acid solution to The addition of zirconium sulfate olution is of a 50-ml volumetric flask. Transfer a sui table aliquot, course omitted, and tbe oxide ignited at 1,0000 C not to exceed 25 ml and containing not more than and weighed as niobium pentoxide. Losses due to 1 mg of tantalum, to the flask, and mix well. incomplete precipitation or solubility do not exceed Dilute to volume with the ammonium oxalate 0.5 mg of niobium. ammonium citrate solution, mix t horoughly, alld d. Tantalum allow to stand 10 min. Place water in a 2-cm photometer cell for use as a reference solution. Reagents Transfer a portion of the test solu tion , prepared as Ammonium Oxalate-Ammonium Citrate Solution. above, to a matched 2-cm photometer cell. Using Add 25 ml of sulfuric acid to 975 ml of water, and the reference solution, adj ust the photometer to the mix well. Add 40 g of ammonium oxalate mono ini tial se t ting using a lig h t ban d cen tered at 400 hydrate and 50 g of diammonium citrate, and warm m". While main taining this photometer adj ustmen t, (30 0 to 350 C) on the steam bath to dissolve the take the photometric reading of t he test solution. alts. Filter through a dry filter, if necessary, to D etermine the amount of tantalum present in obtain a clear solution. the test solution from a calibration curve prepared Pyrogallic Acid Solution (200 g/liter). Dissolve as follows: Transfer with a pipet 25 ml of pyrogallic 100 g of pyrogallic acid in 400 ml of ammonium acid solution to each of four 50-ml volumetric flasks. oxalate-ammonium citTate solution, dilute to 500 Transfer 0.0, 2.0, 5.0, and 10.0 ml of standard ml with the same solution, and transfer to a glass tantalum solution (125 ,ug/ml) to the 50-ml vol stoppered bottle. This solution is not especially umetric flasks, and continue as directed in the stable, and a fresh solution should be prepared if previous paragraph. Plot the photometric readings the blank photometric reading is excessive. Oc of the calibration solutions with respect to micro casional lots of pyrogallic acid have been observed grams of tantalum. The solutions follow Beer's Law, to give a solution which is excessively colored, even but a blank is required to correct for the color con though freshly prepared. tributed by the pyrogallic acid solution. Because Standard Tantalum Solution (1 mloO.125 mg of the variable quality of this reagent, the system

17 of photometric readings is designed to allow poor to in section 3.3.c. Since stable solutions of niobium quality lots to be detected and di scarded. The and tantalum cannot be prepared except through r eaction has a negligible temperature coefficient , but the use of complexing agents, weighed portions of is sensitive to changes in pyrogallic acid concentra the oxides were added to the first ignited cupferron t ion under the conditions specified in the procedure. concentrate. This mode of operation is justifiable If 20 mg or more of tantalum is involved, the deter on the basis that an appreciable part of these mina tion can be conveniently completed by pre elements exists in steel as relatively insoluble cipitation with cupferron as described in the first carbides and nitrides which in any case cannot be paragraph in this procedure. No zirconium addition duplicated by synthetic solution mixtures . A proof is made, and the oxide is ignited at 1,000 ° C and of the concentration step for these two elements weighed as tantalum pentoxide. Losses due to in would require more sensitive methods; possibly the complete precipitation or solubility do not exceed use of active tracers in preparing the steels or ac 0.5 mg of tantalum. tivation analysis of the filtrate would define the lower limit. Since satisfactory replication was ob 4 . Results tained on steels containing as little as 10 ppm of either element , the limit to be established is quite low. Gram portions of high-purity niobium and tan The values for titanium and tantalum shown in talum pentoxides were prepared from commercial table 1 require little commen t, the values being oxides by column elution with hydrochloric-hydro within the limits usually ob tained from photometric fluoric acid mixtures, precipitation with cupferron determinations. The values for zirconium are and ignition. Spectrographic examination of the slightly high, and illustrate the difficulties encoun niobium pentoxide indicated the chief impurities tered in properly washing the zirconium phosphate were boron and silicon. A chemical test made by precipitate [10 , p. 569, footnote 20] . A gravimetric ignition, treatment with sulfuric and hydrofluoric finish for this determination is preferred, as an acids, and ignition, indicated these impurities to be ignited precipitate is available to examine spectro n egligible when using the oxide to prepare synthetic graphically for hafnium. The values obtained on mixtures. Small amounts of silver, copper , calcium, the larger quantities of niobium are slightly low, iron, magnesium and tin were detected spectro due to the loss of a few ten ths of a milligram of graphically and estimated to be less than 0.01 niobium in the precipitation with cupferron from the percen t . A similar examination of t he t antalum eluate complexed with boric acid (section 3.3.c). pentoxide indicated the same impurities, and in Provisional certificate values for NBS Standard addition a very small amount of aluminum. It is Sample 123b are: Niobium, 0.75 percen t; tantalum, likely that at least a part of the impurities that 0.20 percent; and titanium, 0.006 percent . These would ordinarily be removed by column separation values are given to show that small additions of actually represent cont amination from dust dis titanium and zirconium can be recovered sa tis tributed by the central air-heating system , resulting factorily from a stainless steel (type 347) matrix from plastering and painting work done at variou s containing tungsten, molybdenum, niobium, and times in the building while this project was in t antalum. progress. The method was designed to provide values for The results obtained on a series of synthetic titanium, zirconium, niobium, and tantalum in the mixtures made to simulate combinations of interest r ange of 0.001 to 0. 5 percen t, in the standardization are given in table 1. Titanium and zirconium were of a group of spectrographic steel standards con added to the solution of the sample as aliquots of taining additions of 22 elemen ts and the rare earths. standard sulfate solutions prepared from National A part of these data, as well as a few results ob tained Bureau of Standards titanium dioxide Standard on three curren t NBS Standard Samples of steel, is Sample 154a and from the zirconium sulfate referred shown in table 2. In general, these values show

T ABLE l. Values obtained by the recommended procedure f or titanium, zirconium, niobium, and tantalum on synthetic mixtures

'ritanium Zil'conimll N iobium T a nta lnm Sample- n umber W eight of 1---,----1----,-----1----,.-----1---.---,---1 sam ple Added Foun d Added Found Added Found Added F ound

g my my my my my my my my 55d __ . _. ______. ______. __ 5 10.3 10.3 10. 6 10.8 10.7 10. 2 10. 7 10. 7 5bd __ . ______5 l. 25 1. 27 26. 4 26. 7 25.2 b 24. 9 0.50 0. 51 55d ._. ______5 25. 0 25.3 I. 06 I. 18 0.60 0.60 24. 9 b 24. 9 55d _.. ______• ____ _ 5 29.8 29.4 0.52 0. 64 26.3 b 26. 1 0. 25 0.28 5bd_.. ______5 0. 60 0. 60 26. 2 27. 0 0.30 0.30 24. 4 b 24. 3 55d __ . ______25 . 60 . 61 0. 52 0.53 25.8 25. 4 25. 1 25. 3 55d_. ______. ____ _ 25 .25 .26 .53 .57 0.30 0.31 0.25 0. 27 123b ______. ___ . _. ______• ___ . ____ _ 10 . 54 . 05 b 74. 6 19. 7 123b ______. ___ _. __ ... ______10 . 55 . 00 75. 1 19.9 123b ______._. __ . ______10 I. 25 1. 78 1.00 L Ot (0) (0) 123b ______. ___ . ______, 10 0.54 0. 50 G.57 b 74. 3 b 19.5

- N B S Standard Sample. b D etermination finished gravim etrically. c N ot determined .

18 '.r.~13l.g 2. Val1te s obtained by the recommended procedure for tltaniu m, zirconi1!m, niobium, and tantalwn in NBS Standard Samples of steel

'l'itanium Zirconium (+TIf) Niobium 'l"'antalulll Sample Sam ole number weight 'l'ype of stcel Certificate Found Certificate Found Certificate Found Certificate Found value value value value

(J % % % % 10 1d ______% % % % 25 (. ) 0. 0076 (a) < 0. 005 (a) 0.003 (ft) < 0. 001 { . 0075 } { <. 005 } { .003 } { < .001 }18Cr- 9N i 170a . _. __- ______10 . 271 .036 <. 001 < . 001 b O. 28 (ft) (a) }O I)Cn-heartb steel { . 271 }------{ . 036 } { <. 001 } { < . 001 121C______10 . 410 <. 005 . 003 b . 42 (a) (0) (ft) < .001 }18Cr- llN i { . 412 } { <. 005 } { .003 } { < .001 . 038 . 065 . 095 . 036 462 and Jl62 __ __ 15 . 037 . 037 0. 063 . 061 0. 096 . 098 0. 036 . 036 } Low-alloy steel { . 037 } { . 064 } { . 093 } { . 036 . 010 .208 . 192 . 151 463 and 1163 . ___ 10 . 010 .011 (,) . 195 . 195 . 199 . 15 . 157 } Low-alloy stccl { . 012 } { . 197 } { . 194 } { . 152 .207 . 001, .001, 46.; and ]l65. __ . 25 . 20 . 206 (d) (,) . 001 , . 001 .0010 }Low.allO Y stccl { . 208 } { } { . 0013 } { .0010 .260 ----~. 094~~ ~. .286 .230 \67 and 1167 __ __ 10 . 26 . 264 0.094 . 092 0. 29 . 290 .23 . 231 } Low·alloy steel { . 264 } { .096 } { . 287 } { . 225 . 056 <. 01 . 498 . 022 A ...•. •••• ______10 . 055 (') <. 01 (') . 494 (') .023 (') . 056 < .01 .491 .022 }19-9 DL { .056 } { < . 01 } { .489 } { . 022

• Value not certified . b Provisional value . • Value not certified because of uncertaulty of spectrographic homogeneity of the sample. d Value not ce rtified because of poor perform ance of recommended method below 0.01 percent. I e Valuc not ccrtified because spcctrographic method not suffic iently sensitive at presen t. ( Preliminary segregation test samples of forthcoming standard. I . satisfactory replication , except for zirconium in [6] J . L. H ague, E. D . Brown. and H . A. Bright, J . Research t ~lO se ~naterials containing less than 0.01 percent of NBS 53, 261 (1954) RP2542. [7] J. L. Hague, E . E. Maczkowske and H . A. Bright, J . Zll·conmm. R esearch NBS 53, 353 (1954) RP2552. I A quite satisfactory correlation between the [8] J. L. H ague, ASTM Proc. 44, 714 (1944). chemical values was also obtained in setting up [9] R . B. Hahn, Anal. Cilem. 21, 1579 (19'19). [ spectrographic curves; the exceptions were zirconium [10] W . H. Hillebrand, G. E. F. Lundell, H . A. Bright, and J . 1. Hoffman, Appl. Inorg. Analysis 2d ed., p . 588 in the range below 0.01 percent wh ere the perform (J . Wiley and Sons, Inc., New York, N. Y., 1953). ance of the chemical method is POOl', and niobium [ll] L. Ikenberry, J . L. Martin, and W. J . Boyer, Anal. Che m. below 0.01 percent where the spectrographic method 25, 1340 (1953). [12] C. M. Johnson, Iron Age 157, No. 15, 66 (1946). 'I lacks sufficient sensitivity at presen t to be useful. [13] Silve Kallmann (Ledoux and Co., Teaneck, N . J.) private . Sample "A" illustratcs the application of the communication. i procedure to a high-temperature material containing [14] K . A. Kraus and G. E. Moore, J. Am. Chem. Soc. 73, appreciable percentages of molybdenum and tung 9 (1951). sten. It has already been shown [6] that niobium, [15] K . A. Kraus and G. E. Moore, J . Am. Chem. Soc. 73. 2900 (1951). molybdenum, and tungsten can be separated by [16] K . A. Kraus and F . Nelson, Proc. Intern. Conf. Peaceful anion exchange in hydrochloric-hydrofluoric acid Uses Atomic Energy 7, p. 116 (United Nations, N. Y., mixtures, and it is hoped to further investigate mix- 1956). [ turcs of these elements in high-temperature alloys. [17] C. A. Kumins, Ind. Eng. Chem., Anal. Ed. 19, 376 (1947). [18] L. A. Machlan and J. L. H ague, J . Research NBS 59, 415 (1957) RP2812. 5 . References [19] W . R . Schoeller, Analytical chemistry of tantalum and niobium, p . 1 (Chapman and H all , Ltd., London, [1] F . H . Burstall and A. F. Williams, Analyst 77,983 (1952). 1937). [2] M . J . Cabell and 1. Milner, Anal. Chim. Acta. 13, 258 [20] W. R . Schoeller and A. R . Powell , The analysis of min (1955). erals and ores of the rarer elements, 3d. ed., p . 210 [3] W. S. Clabaugh a nd R . Gilchrist, J. Am. Chern. Soc. 74, (Hafner Publishing Co., New York, N. Y ., 1955). 2104 (1952). [21] G. T elep and D . F . Boltz, Anal. Chem. 24, 163 (1952). [4] T . R . Cunningham, Ind. Eng. Chern., Anal. Ed. 5, 305 (1933) . [.5] T. R . Cunningham, Ind. Eng. Chern., Anal. Ed. 10, 233 ( 1938). 'WASHINGTON, July 14 , 1958.