Spectrophotometric Determination of Tantalum in Boron, Uranium, Zircolnium, and Uranium-Zircal oy-2 Alloy with Malachite Green A. R. Eberle and M. W. Lerner U . S. Atomic Energy Commission, New Brunswick Laboratorj,, New Brunswick, N . J.
As PART of a continuing program to develop chemical procedures for the analysis of elemental boron for which stringent impurity specifications exist, a spectrophotometric method was sought for determining tantalum over a wide range of concentrations. Spectrophotometric reagents for tantalum have been listed by Waterbury, Thorn, and Kelly (1). The most commonly used reagents, phenylfluorone (2), hydroquinone ( I ) , and pyrogallol (3) suffer from a lack of either sensitivity or selectivity. Malachite green, used recently by Kakita and Got6 ( 4 ) for the analysis of iron, steel, and niobium, appeared t o be artractive from this standpoint despite the fact that boron is one ofthe few interferences. A n efficient separation of traces of tantalum from relatively large amounts of boron, involving the coprecipitation of tantalum with iron(II1) precipitated with ammonium hydroxide, has been found. This procedure was also effective in separating tantalum from uranium, zirconium, and uranium-zircaloy-2 in the presence of suitable complexing agents. Additional studies of the extraction of the malachite greentantalum-fluoride complex by benzene have also resulted in certain differences between our conclusions and those drawn by Kokita and GotO. EXPERIhlENTAL
Reagents and Apparatus. A standard tantalum solution of 100 pg per ml was prepared by fusing 100.0 mg of thin (0.2 to 0.8 mm thick) sheet with 25 grams of potassium persulfate in a quartz flask over a blast burner. To the cooled melt were added 5 grams of oxalic acid and 100 ml of water. The salts were dissolved by heating and swirling over a flame, and the solution was cooled and diluted to 1 liter. A mixed acid solution was made by diluting 27 ml of 49 hydrofluoric acid plus 7.0 ml of sulfuric acid to 2 liters. This solution was stored in polyethylene. A 0.15% malachite green solution was prepared from Eastman Organic Chemicals No. 1264 designated :is the oxalate salt. A n iron(II1) carrier solution, 2.0 mg per ml, was prepared by dissolving 2.42 grams of ferric chloride hexahydrate in 250 rnl of water containing 1 ml of sulfuric acid. (1) G. R. Waterbury, L. E. Thorn, and R. C . Kelly, U. S . A I . Energy Camm. Rrpt., La-3465, 1966. (2) C. L. Luke, ANAL. C i i E M . , 31, 904 (1959). (3) L. Ikenbery, J. L. Martin, and W. J. Boyer, Ibid.,25, 1340 (1953). (4) Y . Kakita and H. Got&,Ibid., 34,618 (1962).
662 *
ANALYTICAL CHEMISTRY
Quartz- and polyethylene-ware only were used except where noted. In the absence of polyethylene separatory funnels, a convenient technique involving the use of I-lb hydrofluoric acid bottles similar to the J. T. Baker Chemical Co. type is described for the extractions. Procedures. STANDARD C U R V E PREPARATION. T O a 250ml separatory funnel, add 80 ml of the mixed acid solution, 0 to 150 pg of tantalum, 20.0 ml of the malachite green solution, and 50.0 ml of benzene. Equilibrate for 30 seconds. Allow the phases to separate for about 1 to 2 minutes and draw off the aqueous phase as completely as possible. Drain the organic phase into a dry polyethylene bottle, cap the bottle and allow to stand for 15 minutes. Decant a portion into a I-cm cell and measure the absorbance, within 5 minutes after filling the cell, at 635 mp against benzene as a reference to obtain the linear calibration curve. If a hydrofluoric acid reagent bottle is used for the extraction, after equilibration invert the bottle for the phase separation, release the valve slightly, and force out the aqueous phase by squeezing the bottle. Decant the benzene phase into a dry bottle and continue as above. ANALYSIS OF BORON. For boron containing greater than 25 ppni, fuse up to 50 mg of powdered sample with 25 grams of potassium persulfdte in a quartz flask. For 50- to 200-mg samples, use 30 grams of persulfate. Mix the boron and persulfate by swirling, then heat with a blast burner. Swirl the molten salt around the sides of the flask until a clear melt is obtained, generally within 5 to 10 minutes. Dissolve the cooled melt in 50 ml of hot 6 % oxalic acid, and dilute to about 250 ml. Add 4.0 ml of the iron(I1I) carrier solution, heat the solution to boiling, and precipitate the iron with a large excess of ammonium hydroxide. Digest on a hot plate for about 10 minutes, add an additional 2.0 ml of the carrier solution to assist in the coagulation, and after 5 minutes filter on 11-cm Whatman No. 42 paper. Wash the precipitate four times with a hot solution przpared by dissolving 3 grams of oxalic acid in 300 rnl of water and making alkaline to phenolphthalein with aninionium hydroxide. (A glass funnel can be used here for faster filtration and washing.) Transfer the paper to a polyethylene funnel, dissolve the precipitate with four 20-ml portions of the mixed acid solution receiving the solution in a separatory funnel (or hydrofluoric acid reagent bottle), and then bunch u p the paper and press out the remaining liquid. Add 20.0 ml of the malachite green solution, 50.0 ml of benzene, and proceed as described above under standard curve preparation. For boron containing less than 25 ppm, place 2 grams of sample into a quartz flask, add 50 ml of water, warm the solution, and slowly add in small portions 15 ml of nitric acid. When the reaction has subsided, evaporate the solution to near dryness, add methyl alcohol in 5-ml portions and boil off the methyl borate until nearly all of the boric acid is re-
Table I. Recovery of Tantalum in Boron, Uranium, Zirconium, and Uranium-Zircaloy-2 Sample Boron
Sample w el gh t , grams 0.05
0.10 0.20 1.o
Tantalum, ppm Found
Added
200 50 I 00 10 25
2.0
.
1.2
1Ch3
5.9
198 490 987 2020 200
200 5oc 1000 2000
53
102 10.6 24.5 5.6 99
10 0 10 0
10.0
5 c
5.0 1.8 1 .o 1 2
10. i
2.G 50
Figure 2.
IO0 150 TAXT i L U I f .
200
2 so
10 1 .(; 300
pg
Zirconium
2.0 3.0 1 .(! 1. o
Extraction of complex in 50-mI aqueous volumes
with varinin
\nliirnpq
of henwne
Uranium-Zircaloy-2 moved. Add 3 :nlof sulfuric acid and 5 mi of nitric acid and e\aporate to dense fumes. When the solution is fuming, add 1 to 2 nil of nitric acid down the side of the flask. Fume off the nitric acid, add 50 ml of methyl alcohol, and evaporate the solution on a steam bath. Finally, fume the solution to near dryness. coo!, a,jd 2 5 grams of potassium persulfate and continue with the f L sion and subsequent steps as described above ANALYSIS OF LJiwwx, Convert metal samples to U 3 0 E ti:\ ignitim and fuse up to 5.9 grams of oxide in a quartz fi'isk with 30 grams of potassium persulfate. Dissolve the cooled melt in 100 rnl of hot 3z oxalic acid, and dilute to 250 ml. Add 4.0 mi of the carrier solution. heat the solution ric2:r boiling. and add ammonium hydroxide slowly with m i ' : a light uranium precipitate does not redissolve. u d i : e d amnioniuni carbonate in small portions to : e d ! s s u ; ~ ct h e piecip rate. then add about 2 grams in excess. Precipi:ate tht iron(lI1) and continue as described for the boron Ixocedui :~, A L A L Y S I S O F % r R U I X i L \ l A S P LTRANILL1-ZIRCALOY-2 ALLOY. Dissolve u p to L grains of metal suspended in 50 ml of water b) the slow addit;o? of 10 ml of 4972 hydrofluoric acid.. Dissoi\,e an!' black :,esidue remaining by adding 1 gram of :iotassiurn persulfate Add 250 mi of boiling water anci 4 1: m: o f the carrier soiciion. If the iron content of ?he sampi, : S !-,I?!:. decrease th: c:trrier quantity b! a 3:srwsponc!r.i,, :!r ~ i c ii n . '4d d ii rnm s n i iim 11) d r oxide ur.ri! :he irsn precipitxres. A \ o i d a iargeexce , f! urC1?iLm i > pi'esei;r is thv r o x i d e :iiiiij the iror ti' " tG: solurinr. i . ! k a i ! i j e . :,nd :her .:rd:! 2 gram:, l: e x x i i t!raI!:L!:7.! in s3iu:.o:: Fi1:f.i- :I;C prezipi M'hatm:ir. N O , 42 ;):!?e: o n ;i po1)e:hyiene; ?.innc;! and COP .. r,:,ve ah ilcicri5ec ioi 111e ho:on DiosILddre (
I
5.0 2.0 1 .a
0.26 0.2s 49.;
0 Q
53 5C
50.1
I .0 2.0
1.3 1.9
2 5
2.7 10.4 39.4 48.7
10 40 50 5G 1WJ
48,7
100.6
76,000 1s. 2'3,000.In the present work, the same conditions were s\ed and nearly identical molar absorptivities were obtained However, extractions of various quantities of tantalum under the conditions of pH, hydrofluoric acid, and malachite green concentrations recommcnded by Kakita a n a Go$ into various amounts of benzene, showed that the mir:!n;uiii aqueous to organic ratio for complete extraction i - .i : 2 Figure 1. When this ratio i j used, a true molar apxorulivity of 104,000 is obtained. Xylene was a less efficier.: extractant and 1,I .I-tl-ichloroetliane a more efficient ext; actant than benzene, but as dibcussed below, trichloros blanks that are high and erratic. Although the exi-xciion described in the proposed procedure is incomplete bei::~ise c!i the necessary aqueous to organic ratio of
,
I .
' ,
b) fine droplets af aqwocls pixise in the benzcne l ' ~ ~j ,filrration ~ m ~proced:ires v,erc led to remove
'3.1
17
After the 15-minute standing period, the absorbances may decrease 0.002 t o 0.005 unit but are essentially constant for another 15 minutes. However, after a 60-minute standing period, the values for the blank and for less than 25 pg of tantalum have decreased significantly while those for more than 25 pg have increased. These changes apply t o readings made with fresh loadings of the cell from the bottle holding the benzene extract. (With the same solution in the cell, absorbance increases occur more rapidly.) A reasonable explanation of these changes may be made by considering that absorbance decreases occur as more droplets of water fall out of the benzene, and absorbance increases occur as the leuco base, which is soluble in benzene, is oxidized. In addition t o the interferences listed by Kakita and GotG, it was found that chromate and molybdate interfere directly. These elements are eliminated by the precipitation separation. Reduction of the chromate also eliminates the interference. Elimination of boron by volatilization as the trifluoride with sulfuric acid in platinum caused erratic absorbance readings; accordingly, fuming in platinum should be avoided. Other interferences include large amounts of those elements pre-
cipitated as the fluoride during the extraction step making phase separation difficult. Various quantities of tantalum were added to tantalum-free boron, U308,zirconium, and zircaloy-2. The results are shown im Table I. I n the analysis of 5-gram samples of uraniumzircaloy-2, insoluble fluorides precipitated during extraction make phase separation difficult. A double precipitation still yields some insoluble fluorides but phase separation can now be made. With 2-gram samples, this difficulty is not encountered. The efficiency of the iron(1II) hydroxide carrying of the tantalum apparently depends on activation or solubilization of the tantalum with oxalate or fluoride prior to the precipitation. In the absence of oxalate or fluoride, the recovery of the tantalum is incomplete and variable. This same type of activation is necessary in the determination of silicon a s the reduced heteropoly acid (5). RECEIVED for review January 5 , 1967. Accepted February 16, 1967. (5) A. B. Carlson and C. V. Banks, ANAL.CHEM., 24,472 (1952).
Quantitative X-Ray Fluorescence Analysis of Polycrystalline Yttrium Aluminum Iron Garnet Y. S. Kim Bell Telephone Laboratories, I n c . , 555 Union Blrd., Allentown, Pa. CHEMICAL ANALYSIS of major and minor elements by x-ray fluorescence is used extensively by industry, This method can be rapid, accurate, and precise. As in other methods of instrumental analysis, the accuracy and precision are limited by the sensitivity and reproducibility of the instrument and the quality of the prepared standards and samples. Several recommended techniques are described by Liebhafsky et a l . ( I ) . In preparing polycrystalline yttrium aluminum iron garnet (Jn this text yttrium aluminum iron garnet will be abbreviated by YAIG or simply garnet..), the stoichiometry of the garnet influences both the physical and electromagnetic properties (2-4). Optimum electromagnetic properties are shown by garnets whose composition is virtually stoichiometric ( 5 ) . TO acfiieve necessary physical homogeneity and particle size reduction, calcined garnet mixes are ball-milled. During the ball-milling operations, iron, abraded from the balls and ballmill, is added to the garnet powder. This can amount to about 0.5 t o 1 weight of the total mix. Recently, a technique has been developed (6) t o control the relative iron pickup in the garnet preparation process. The technique is reliable. However, it is slow and requires sound engineering judgment to be exercised. I t was desired to develop an x-ray fluores(1) H. A. Leibhafsky ef a/., “X-ray Absorption and Emission in Analytical Chemistry,” Wiley, New York, 1960. (2) S. Geller et a/., Phys. Rec., 110, 73 (1958). (3) Berteaud et a/., Compt. Rend., 250, 3807-9 1960. (4) K. P. Velv et a/., Societ Phyys. JET‘, 36 (9), No. 5:1138-9 November 1959. ( 5 ) L. G . Van Uiter et a / . ,J. Appl. V., 130, 363, 1959.
(6) H. M. Cohen and R. A. Chegwidden, J. Appl. Phys. Suppl., April 1966.
664
ANALYTICAL CHEMISTRY
cence technique t o analyze the iron content, to within 0.1 weight of the amount of iron present, of samples which were withdrawn from a continuously revolving ball-mill. This would allow the determination of the exact point at which enough abraded iron was added t o the mix to adjust its composition to the proper stoichiometry (6). It has already been shown that x-ray fluorescence analysis is a rapid and reliable method to analyze ferrite materials (7). This paper reports the development of a method of x-ray fluorescence analysis which is capable of determining the amount of Fe2O3in garnet with a precision of 0.1 weight Fe203. (The garnet composition Y&11.25Fe3.75012, discussed in this text, contains approximately 41.07 weight iron.) To gain such precision, long counting intervals are necessary. Thus, in developing the analysis technique, it is of utmost importance t o quantitatively ascertain the stability of the equipment and define potential sources of error in the measurement of the relative intensity of the fluorescent radiation.
z
z
z
EXPERIMENTAL Analyses were performed on G E XRD-6 x-ray machine using chromium radiation instead of tungsten radiation. A LiF crystal was used for the analyses. The chromium radiation was selected because it was convenient to analyze both transition elements and light elements (Al, Mg, etc.). FeKBI1 and Y K r I I were chosen for the analytical lines because no interference occurred, and the peak-to background ratio was found to be excellent. (7) A. E. Kott, The Engineer, Western Electric Co., New York, July 1964.
