tered in igniting powdered samples in this way, it may be necessary to increase the furnace power with the grid current t a p switch. I n the procedure described, the calibration of the conductivity cell is accomplished by combustion of measured amounts of either potassium acid phthalate or NBS 55e. This calibrating procedure, however, does not disclxe the degree of carbon recovery frJm the tungsten sample, and this is necessary to place the determination on a quantitative basis. The validity of reporting carbon in tungsten, based on recoveries from iron, steel, or organic compiunds, appeared to warrant further testing because these procedures are based on the assumption that the carbon contents of the metal sample and the calibrating material are totally evolved. Recovery experiments were designed to assess effectiveness of the evolution of trace amounts of carbon from tungsten metal, with the direct-combustion procedure, by doping samples with near stoichiometric WC and W2C. The carbides of tungsten were chosen because it appeared they would most nearly simulate the chemical nature of carbon in tungsten. The combustiongravimetric value for carbon did not significantly deviate from the stoichiometric value and the latter was therefore used in calculating quantities of carbon. T o facilitate weighing microgram amounts, the powdered carbides were blended with pure tungsten powder containing less than 10 p.p.m. of carbon to form a mix containing approximately 1% carbon by weight. The additional tungsten added to the crucible with the carbides was negligible and did not require a correction.
The experimental procedure consisted of adding a few milligrams of the WCtungsten or R2C-tungsten mixtures directly to a refractory crucible. The carbides were then covered with 2 grams of the tungsten-base material, which was prepared from electron-beam melted tungsten that produced a signal of 0.4 ohm for a 2-gram sample. Table I1 is a summary of recovery experiments for WC and W2C and includes comparative data for potassium acid phthalate and the iron standard, S13S 55e. The recoverieh from the carbides were coniistently greater than those obtained for the organic compound or the standard iron sample and may have been caused by slight differences in the blank corrections for the different procedures. The deviations were not considered significant for the purposes of this experiment, which adequately demonstrates the accuracy of the direct combustion procedure. Precision studies were made on 4gram samples of tungsten metal containing about 4.0 p.p.m. carbon. The relative standard deviation calculated for 10 determinations made over a period of one week was 12%. This improved precision results from the use of increased sample weights and a more constant blank. Since this method is successful in determining the carbon content in tungsten, the extension of the directcombustion method to metals such as molybdenum, tantalum, niobium, zirconium, titanium, chromium, and copper is also of interest. These metals will couple directly if the particle size is similar to that described for tungsten. For these more ductile metals it is often necessary to provide the proper size
by cutting or shearing. In sheet form up to l / , 6 inch in thickness, these metals couple and oxidize especially rapidly by placing a section in the bottom of the crucible with the sheet oriented perpendicular to the axis of the induction coil. Complete oxidation is observed for molybdenum only if the sublimation of molybdic oxide is allowed to go to completion. I t appears, therefore, that a special trapping device is desirable to prevent contamination of the conductometric system by the volatile oxide. Tantalum, niobium, zirconium, titanium, chromium, and copper undergo fubion of the oxides similar to tungsten. Preliminary recovery experiments using TaC and S b C in the metals indicate quantitative recover-y of carbon under the conditions described for tungsten. LITERATURE CITED
(1) Edwards, G. W., Linde Co., Division of Union Carbide, Indianapolis, Ind.,
private communication, 1962.
( 2 ) Elwell, JV. -,T., Wood, D. F., “The
Analysis of Titanium, Zirconium and Their Alloys,” p. 23, Wiley, 1961. ( 3 ) Haymes, J. E., Ollar, A., Bureau of Mines RI-6005, p. 17 (1962). ( 4 ) Huber, F. E., Chase, D. L., Chemist Analyst 50, 71 (1961). ( 5 ) McKinley, T. D., Advisory Group for Aeronautical Research & Development Working Paper M-33, Analysis of Refractory Metals. (6) Stephens, J. R., AIME Meeting, October 28-November 2, 1962. WILLIAMA. GORDON JUDSON W. GRAAB ZITAT. TUMNEY Lewis Research Center National Aeronautics and Space Administration Cleveland, Ohio 44135
Separation and Determination of Uranium in High Zirconium Alloys SIR: The need for the quantitative estimation of uranium in zirconiumaluminum alloys arose from pyrometallurgical studies on the purification of uranium in zirconium-uranium alloys. The determination of microgram quantities of uranium in the zirconium alloys (Zr.%ls) posed a problem because of the high mole ratio of zirconium to uranium of approximately 6 X lo4. Several spectrophotometric procedures have been reported f6r the determination of uranium in the presence of large amounts of zirconium ( 2 , 6 ) . The procedure reporting the highest tolerance for zirconium states that zirconium interferes when the zirconium-touranium mole ratio exceeds 2.4 X l o 3 (5). A fluorometric procedure is reported for the determination of uranium in zirconium metal (’7). This procedure 1398
ANALYTICAL CHEMISTRY
uses ethyl acet,ate as an extractant and appreciable zirconium is extracted with the uranium. The quenching of uranium fluorescence due t,o the extracted zirconium is compensated for by making a standard addition of uranium to an aliquot of the sample being analyzed. Thus a technique which would quantitatively separate uranium from zirconium and eliminate quenching would be desirable. h comprehensive discussion of separation procedures for uranium is given in the treatise (4). The desired species, when present as a trace constituent, is usually separated from the ‘matrix. In some instances, large quantities of impurities are removed from the desired constituenti.e., solvent extraction of impurities from uranium(ITl) by cupferron or diethyldithiocarbamate. However, removal of matrix quantities by precipitation is not
common because of loss of the desired species by coprecipitation. K e have used the bromomandelic procedure to separate fission-product zirconium plus carrier zirconium from an aluminum-magnesium matrix. The zirconium bromomandelate precipitate carries approximately 11% of the niobium-95 and less than 1% of fissionproduct strontium, yttrium, ruthenium, or cerium. h study of the coprecipitation of uranium by the bromomandelate precipitate was made to evaluate the possibility of a direct determination of uranium in the filtrate. EXPERIMENTAL
Apparatus. An Atomic 1095 Scalcr equipped with a 27r flow counter was used for alpha counting. The fluorometer has been described ( 1 ) .
Reagents. ALUMINUMNITRATENITRICACID SOLUTION. Dissolve 110 Table 1. Uranium Recoveries from Synthetic Zirconium-Uranium Mixtures grams of reagent goade aluminum (127 milligrams of zirconium taken) nitrate nonahydrate [Al(N03)3.9H20] in 150 ml. of water. Add 80 ml. of conRange Type of Kumber Per cent centrated nitric acid. Cool, transfer to Type of uranium measure- determiuranium Rel. std. a 250-ml. volumetric flask, dilute to separation taken, pg. ment nations recovered dev., % volume with water, anti mix. Bromomandelate TRI-n-OCTYLPHOSPHINE OXIDESOLU100.5 A2.3 precipitation 20.0 F 10 TION, 0.1 MOLAR. Dissolve 3.866 grams Bromomandelate 51.5 A 2 100.39 f0.27 precipitation of E.K.-7440 tri-n-octylphosphine oxide Bromomandelate in Skelly solvent (boiling range of 100' 51.5 97.86 f1.92 precipitation F 2 t o 190' C.) and dilute to volume with Bromomandelate Skelly solvent. 51.5" 98.25 f2.47 precipitation F 2 URANIUMSOLUTION. Dissolve 1.765 Bromomandelate grams of C.P. grade uranyl sulfate tri97.09 f0.92 precipitation 30. ga F 2 hydrate in 20 ml. of concentrated Bromomandelate 100.0 f3.2 nitric acid and dilute t o 1 liter. One precipitation 15.45a F 2 Bromomandelate milliliter contains 1.00 mg. Store in a precipitation 10.30 A 2 98.54 f0.69 polyethylene bottle. Make appropriate Bromomandelate dilutions for working solutions. 97,09 f1.36 precipitation 10.30 F 2 ~ R A N I U M SOLUTION. - ~ ~ ~ A standard Bromomandelate solution of uranium-233 was available 97.09 f2.87 5.15 A 2 precipitation which contained 1.031 mg. of uraniumBromomandelate 233 per ml. and had a nitric acid con99.51 A1.79 5.15 F 2 precipitation centration of 5y0. Tkis stock solution Cupferron 94.08 f1.20 extraction 20.6 A 3 was prepared from uranium-233 metal obtained from Los Alamos (98y0 P3). A = Alpha count. Four T counting gave a half life of 1.71 F = Fluorometric. x 1oj years. Tracer solutions were prepared by appropriate dilution of the Measurement made in the presence of bromomandelic acid. standard solution a n j made 5% . - in nitric acid. ZIRCOXIUM SOLUTION. Dissolve 38.2 grams of zirconium nitrate dihydrate Table II. Determination of Uranium in Aluminum-Zirconium Alloys rn 50 ml. of water and dilute t o i liter. Zirconium Y One milliliter contains approximately y Uranium found present, uranium 13 mg. Standardize by bromomandelic Sample grams added Gross Net acid procedure (6). 1 0.347 . . . 2 3 . 0 2 3.0 Procedure. Synthetic solutions 0,347 20.0 42.5 22.5 were prepared which cmtained 127 mg. 2 0,280 ... 49.9 49.9 of zirconium and varying quantities of 0.280 20.0 71.5 51.5 uranium-233. The zirconium was pre3 0.390 ... 31.0 31 .O cipitated by the broniomandelate pro0.390 20.0 52.0 32.0 cedure (6). The precipitate was washed 4 0.278 ... 71.5 71.5 six times with 10-ml. portions of hot 0.278 20.0 90.6 70.6 water and the filtrate and washings were combined and diluted t o a n appropriate volume. Aliquots for alpha counting were evaporated on planchets and then heated to destroy the organic RESULTS AND DISCUSSION funnels, and diluted t o 40 ml. Two matter. Duplicate aliquots were anmilliliters of a 6% solution of cupferron alyzed fluorometrically after they were were added to each sample and the The results on the determination of evaporated t o dryness and the organics samples were shaken for approximately uranium in synthetic samples conwere destroyed by a sidfuric-nitric acid 30 seconds. The cupferrate was then taining zirconium and uranium are wet oxidation. extracted with 10 ml. of chloroform and given in Table I. The fluorometric procedure involved the chloroform layer was drawn off. Aluminum-zirconium alloys cona trioctylphosphine oxide (TOPO) exCare was taken t o leave a small amount traction ( 8 ) , micropipetting of a 100-ctl. taining 34% zirconium were dissolved of chloroform remaining in the separaaliquot of the organic phase onto a in 1 : 1 hydrochloric acid. Five to 10 ml. tory funnel. The cupferron addition carbonate-fluoride flux (S), muffle fusion, and chloroform extraction was repeated of nitric acid were added to the hot and fluorescent measurement ( 1 ) . seven times. (Complete extraction of solution to ensure oxidation of uranium The effect of bromomandelic acid on zirconium was noted by the fine white to uranium(V1). riliquots were diluted the extraction and fluorometric meascrystalline appearance of the cupferron to reduce the acidity to approximately urement of uranium was evaluated. in the aqueous phase.) The aqueous one molar. The zirconium was preSynthetic samples containing natural phase was then washed twice with 10cipitated as the bromomandelate as uranium and zirconium were carried ml. portions of chloroform. Five millidescribed above. Aliquots of the filtrate through the above separation procedure. liters of nitric acid were added to the Aliquots from the fill rate were taken were taken for TOPO extraction and aqueous phase and the solution was for TOPO extraction and fluorometric fluorometric determination of uranium. evaporated t o dryness. The residue determination. For icomparison purwas dissolved with 2.5 ml. of nitric acid Additional aliquots were spiked with poses cupferron was used t o separate and transferred to a 25-ml. volumetric 20.0 y of uranium prior to the precipitazirconium from uranium. flask. The beakers were rinsed with tion of zirconium. The data are shown Three synthetic solutions containing 2 ml. of hot nitric acid and the rinsings in Table 11. 127.8 mg. of zirconium and 20.6 ctg. were added to the volumetric flasks. The data from Tables I and I1 show of uranium-233 were treated with 2.5 One-milliliter aliquots of the filtrate that uranium(V1) is not coprecipitated ml. of sulfuric acid. The solutions were taken for alpha counting. These by zirconium bromomandelate. The were evaporated until fumes of sulfur aliquots were evaporated on planchets presence of bromomandelic acid in the and the planchets were flamed t o detrioxide appeared and then they were filtrate has no effect on the fluorometric stroy any organics. cooled, transferred t o 125-ml. separatory VOL. 36, NO. 7, JUNE 1964
1399
determination of uranium. The absence of coprecipitation of uranium, when zirconium is precipitated as the bromomandelate, is rather unusual. It is general practice to remove a trace constituent from the matrix rather than remove the matrix from the trace constituent. The precipitation of the zirconium as the bromomandelate gives a direct determination of zirconium and in addition yields a quantitative separation of uranium for subsequent fluorometric determination. K h e n the zir-
conium was removed by a cupferron extraction, the uranium recoveries were low. LITERATURE CITED
(1) Byrne, J. T., ANAL.CHEM.29, 1408 (19573. ( 2 j Gill,’ H. H., Rolf, R. F., Armstrong, G. W’.,Zbid., 30, 1788 (1958). (3) Grimaldi, F. W., Fletcher, M. I.,
Titcomb, J., I:. 8. Geol. Survey Bull. 1006 (1954).
(4),Kolthoff, I. M.>Elvirlg, P. {;, “Treatise on Analytical Chemistry, Part 11,
5’01. 9, pp. 30-59, Interscience, Kew York, 1962. (5) Maeck, W J., Booman, G. L., Elliott. M , C.. Rein. J. E.. ~ ~ K A L
.
C H E M . ’ 1130’119593: ~~. (6) Papuci,’ R. A4.,Klingenberg, J. J., Zbid., 27, 835 (1955). ( 7 ) Vozzella, P. A,, Powell, A . S.,Gale, R. H., Kelly, J. E.,Zbid., 32, 1.230 (1960). (8) White, J. C., U. S. Atomic Energy
Comrn. Rept. ORNL-2161 (1956).
R. F. ROLF Kuclear and Basic Research Laboratory The n o w Chernical.Co. Midland, Mich.
X-Ray Fluorescence Lead-Uranium Ratio Measurements in Allanite, Ban kuru District, India SIR: il preliminary investigation of the mineral allanite has been made to see if the x-ray fluorescence method is satisfactory for age determination. An approach through the chemical method had been made by Aswathanarayan ( I ) , Sarkar ( 7 ) ,and Xandi and Sen (6). Allanite occurs as an accessory mineral in siliceous and intermediate igneous rocks. The mineral is monoclinic and varies in color from light brown to black. Allanite is a member of the epidote group, with rare earths substituting for calcium. It is often found beside or intergrown with epidote. The metaniictization of allanite produces an amorphous alteration product and some allanite from pegmatite is completely isotropic. The alteration is inferred to be the result of destruction of the crystalline structure of allanite by radioactive decay of its uranium and thorium. The allanite samples analyzed came from Madhapur-Tilaboni area, Bankura District, India. They were more or less fresh and unaltered. A few metamict grains were associated with fresh non-
metamict varieties. All samples studied were optically negative.
rected peak heights, and in Table I the values are compared with rewlts obtained earlier by chemical methods.
EXPERIMENTAL
Sample Preparation. Mineral speci-
mens were ground to 200 to 300 mesh size, quartered, and thoroughly mixed with 200- to 300-mesh metallic bismuth which served as a n internal standard for the determination of C , T h , and P b . Procedure. For this stud\-, ueak heights rather than quanta” counts were used. Recorded peak heights were corrected for the background in the usual way. For all runs, scaler was set a t 4, multiplier a t 0.6, and time constant a t 4 seconds. Scanning was done a t per minute. The mi\ture was wbjected to a primary tunghten radiation and the fluorescent radiation wa.; picked up and recorded by a Philips x-ray fluorescence spectrograph. Elements were identified by the Bragg angles of their wavelengths. In five allanite samples a n alyzed, the elementq present were L-, Th, P b , M n ) Fe, La, Ce, and Ti. Percentageh of the elenienta P,Th, and P b were calculated from the cor-
RESULTS
Lead-Uranium Ratio. Pu-U ratio calculated from results listed in Table I was used in calculating the age of the mineral. I n the relation Age = Pb/’(U K . T h ) C , the constant K is not accurately known. For minerals of mid-Paleozoic era, K is generally taken as 0.333 (4). Using K = 0.380 and C = 7400 ( 7 ) , the age comes out as equal to 1475 million years, which is in fair agreement with values obtained earlier from chemical analyses of this mineral ( 6 ) .
+
ACKNOWLEDGMENT
K o r k reported here was carried out a t the Sational Professor’s Laboratory, Calcutta. The authors express their gratitude to S. S . Bose, F.R.S., and S . S . Chatterjee, Head of the Department of Geology, Calcutta University, for many suggestions and discussions, and for the interest with which they followed the work. LITERATURE CITED
Table I.
Comparison of U, Th, and Pb Analyses of Allanite b y X-Ray Fluorescent Spectrometry and by Chemical Methods
0.021
0.31
0.002
,..
1.56
..
Present results, X-RFS Aswathanarayan (1)
Xandi and Sen ( 6 ) Hutton ( 2 , 3 ) Hutton ( g ! 3) Marble ( 5 ) Marble ( 6 )
1400
ANALYTICAL CHEMISTRY
(1) Aswathanarayan, U., Proc. I n d i a n Acad. Sci. 38, 226 (1953). ( 2 ) Hutton, C. O., A m . J . Sci. 249, 208 (19511. ( 3 ) Hutton, C. O., Am. Mineralogist 36, 223 (19511. (4) Keevil, K.B., Zbid., 35, 816 (1950). (5) hZarble, J. P., Zbid., p. 845. (6) Xandi, S.K., Sen, I). K.,J . Sci. Znd. Research (India)9 , 12p (1950). 1 7 ) Sarkar. P. B., Scz. Cult. (Calcutta) 7, 118 (1941)
S. B. BHATTACHERJEE M.X. KUMAR University College of Science Department of Pure Physics 92, Acharyya Prafulla Chandra Road Calcutta 9, India
