The precision of a single analysis was determined for each of two lots of Tween 80 and Emulphor EL 620. Ten replicates of 125 mg of surfactant were added to the reaction mixture, as described in the previous paragraph, and the molybdenum absorbance in the flame was measured. The mean standard deviation and relative standard deviation of the surfactant found was calculated (7). The amount of surfactant found was calculated from the regression coefficients for the batch (Table 111). The precision of a single analysis was calculated from experimental values obtained under virtually uniform conditions in two consecutive working days (Table IV). The precipitation procedure was carried out on equal weights (125 mg) of each of the different surfactants and the molybdenum absorbance values of each of the residual reaction mixtures measured. The values, shown in Table V, show that the quantity of molybdenum reacted is quite different for each surfactant. Optimum ratios of reaction mixture to surfactant must be determined for each surfactant type, to ensure a linear relationship between molybdenum absorbance and weight of surfactant used. These results show that the concentration of nonionic surfactant in solution can be measured by determining the molybdenum concentration in the residual reaction mixture (7) C. Mack. “Essentials of Statistics for Scientists and Technologists,” Plenum Press, New York, 1967.
by atomic absorption spectrophotometry. However, as in the classical method of measurement ( I , 2), the nonstoichipmetric nature of the reaction between the surfactant, barium chloride, and phosphomolybdic acid means that the empirical relationship between the amount of phosphomolybdic acid reacted and the amount of surfactant present can only be determined when the type of surfactant and the composition of the solution containing it is known or a placebo is available. Table I11 gives some indication of variation in empirical factor to be expected between batches of the same surfactant, Table V the variation between types of surfactants, and Table I the variation due to changes in the inorganic composition of a multicomponent solution which contains the surfactant. Valid quantitation can be achieved only by a comparison of samples and reference standards prepared from the same batch of surfactant and analyzed in an identical multicomponent system. ACKNOWLEDGMENT We thank A. G. Whittaker, systems analyst of HoffmannLa Roche, Nutley N. J., for the statistical analyses except those reported in Tables 111 and IV. We also appreciate the assistance of E. H. Waysek in carrying out atomic absorption measurements.
RECEIVED for review July 22, 1968. Accepted October 16, 1968.
Determination by Atomic Absorption of Molybdenum, Ruthenium, Palladium, and Rhodium in Uranium Alloys J. M. Scarborough Atomic International, Canoga Park, Gal$ 91304 The feasibility of determining Mo, Ru, Pd, and Rh in uranium alloys by atomic absorption spectrometry was investigated. The mutual interference of the four elements which is normally a complicating factor in the determination of these elements by atomic absorption was eliminated by the presence of uranium. A procedure for the analysis of uranium fissium is presented.
MANYCOMPLEX URANIUM alloys have been compounded for use as nuclear fuel. Uranium fissium, made up of uranium molybdenum (2.46 ruthenium (1.96 %), rhodium (95 (0.28 Z), palladium (0.19 zirconium (0.10 Z), and niobium (0.01 is one of these alloys, the properties of which are reported elsewhere ( I ) . The analytical chemistry of the alloy, involving traditional techniques, has been thoroughly investigated (2, 3). Recently, the need arose to provide methods of analysis for this alloy which would be faster, cheaper, and, if possible, more reliable than the existing methods for determining Mo, Ru, Pd, and Rh. Atomic absorption spectrophotometry, which
x),
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x), x),
(1) S. T. Zegler and M. V. Nevitt, “Structures and Properties of Uranium-Fissium Alloys,” A E C Report, ANL-6116, (1961). (2) J. 0. Karttunen, ANAL.CHEM., 35, 1044-69 (1963). (3) C. J. Roddin, Ed., “Analysis of Essential Nuclear Reactor
Materials,” Division of Technical Information, USAEC (1964), pp 456--60. 250
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had not been considered for the analysis of fissium previously, offered a promising approach to the problem. A significant amount of information is available on the determination of Mo by atomic absorption techniques; however, very little new information has been forthcoming since the work of David reported in 1961 ( 4 ) . Mostyn and Cunningham (5) later reported on interferences associated with the determination of Mo in ferrous alloys. References to the determination of Ru, Pd, and Rh are somewhat more limited. The works of Lockyer and Hames (6) and Menzies (7) on the determination of the noble metals, discuss the determination of Pd and Rh. That of Strasheim (8) treats interferences in some detail. Peter Heneage ( 9 ) and Deily (IO) reported on the determination of Rh. Erinc and Magee (11) discussed the determination of Pd using propane flames. (4) D. J. David, Analyst, 86,730 (1961). ( 5 ) R. A. Mostyn and A. F. Cunningham, ANAL.CHEM., 38, 121
(1966). (6) R. Lockyer and G. E. Hames, Nature, 189,830(1961). (7) A. C. Menzies, ANAL.CHEW, 32, 898 (1960). (8) A. Strasheim, Appl. Spectry, 17, 65 (1963). (9) Peter Heneage, Atomic Absorptiorz Newsletter, 5, NO. 3, MayJune 1966. (10) James R. Deily, ibid., 6 , No. 3, May-June 1967. (11) G. Erinc and R. J. Magee, A m l . Chim. Acta, 31, 197 (1964).
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Figure 1. for Mo
Effect of Ru, Pd, Rh, and U on absorbance values
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Figure 2.
Effect of Mo, Pd, Rh, and U on absorbance values
for Ru
Atomic absorption spectrophotometry has not been widely applied to the analysis of uranium alloys; therefore, the works of Humphrey (12), Jursik (13),Goleb (14), and Walker (15) are worthy of notice. Although it has been demonstrated that Mo, Ru, Pd, and Rh can be determined individually by atomic absorption techniques, several uncertainties still exist in terms of the mutual interferences of these elements and the effects of various anions and cations. No information is available on the effect of uranium in a sample matrix containing these elements. Therefore, this investigation was designed to study the possible mutual interference of Mo, Ru, Pd, and Rh; to establish the effect of uranium on the absorbance values for these elements; and to develop an analytical procedure for the analysis of fission alloy. EXPERIMENTAL
Standard Solutions. Standard stock solutions (nominally 10 mg metal per ml) of Mo and Pd were made by dissolving accurately weighed quantities of the metals in appropriate mixtures of HC1 and “Os and diluting with water. Hydrochloric acid solutions of RuCla and RhCl3 (10 mg metal/ml) were standardized gravimetrically by reduction of the cations to metals with magnesium. Uranium stock solutions were prepared by dissolving UOs in HCl containing a small amount of “Os. (12) J. R. Humphrey, ANAL.CHEM., 37, 1604 (1965). (13) M. L. Jursik, Aromic Absorption Newsletter, 6 , No. 2, MarchApril 1967, (14) Joseph A. Goleb, ANAL.CHEM., 35, 1978 (1963). (15) C. R. Walker and 0. A. Vita, “Analysis of Impurities in Uranium Compounds by Atomic Absorption,” AEC Report, GAT-T-1470 (Nov. 1967).
Sample Preparation. Accurately weighed 4-gram samples of fissium alloy were placed in 400-ml Teflon beakers and covered with 20 ml of water. Sixty ml of a 5 : l HCl/HN03 mixture and 10 drops of concentrated HF were added rapidly to the sample and the beaker was covered. The samples dissolved rapidly, within 3-4 minutes. (See reference 3 for a discussion of dissolution procedures.) The resultant solutions were diluted to 100 ml with water and stored in polyethylene bottles. Suitable aliquots were diluted for analysis. In this investigation, samples were analyzed at several concentrations for the purpose of observing the influence of sample concentration on the results. Instrumental Parameters. Although the Boling burner has not been recommended for use in the determination of Pd and Rh (9), it was used throughout this work following preliminary investigation. In the preliminary survey it was noted that the 3-slot Boling burner provided better stability in the absorption measurements for all elements of concern than did the single slot premix burner. It has been established that very fuel rich flames give the highest sensitivity for the determination of Mo, but as David (4) found, better results were obtained by sacrificing some sensitivity to gain stability by reducing the fuel content of the flame. It was also found that carbon deposits on the burner were not a problem when only moderately fuel rich flames were used. Therefore, the fuel/air ratio (10/7) for Mo was simply adjusted to produce reasonable absorption values. Fuel to air ratios for Ru (10/8.5) and Pd (9.5/9.5) were adjusted to give a little less than maximum response for solutions containing 50 ppm of the metals in order to provide a margin of flexibility for reproducing calibration curves in later work. As reported by Heneage (9), Rh sensitivity was observed to increase with flame temperature. Since the 3-slot Boling burner could be damaged by a very hot flame, the fuel/air ratio was arbitrarily set at 9.5/9.5 to VOL. 41, NO. 2, FEBRUARY 1969
0
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Figure 3. for Pd
Effect of M o , Ru, Rh and U on absorbance values
provide a sensitivity value for Rh comparable to values observed for the other elements. Optimum burner height was found to be about 5 mm below the lower edge of the light beam for all measurements. A slit width of 0.1 mm provided the best balance among Sensitivity, noise, and linear response. Lamps operated best at currents very close to the values recommended by the manufacturer. All samples were aspirated at the rate of 3.8 ml/min. Wave lengths used for Mo, Ru, Pd, Rh were 3133, 3499, 2476, and 3435 Angstroms, respectively. RESULTS AND DISCUSSION
The calibration curves for pure standards in 0.1N HCl are shown in Figures 1,2, 3, and 4. Appropriate mixtures were prepared to determine the extent of mutual interference among the four elements. Table I summarizes these effects in binary mixtures containing 20 ppm of each element. Absorbance values for mixtures containing equal concentrations of all four elements are also plotted in Figures 1-4. The problem of mutual interference is effectively illustrated by these data. It should be noted that these observations are somewhat different from those made by Strasheim (8) whose findings also differed somewhat from those of Lockyer (6). The presence of uranium in samples is a variable in this work which was not encountered by other investigators. Therefore, the absorbance of standard solutions of the individual elements containing uranium and the absorbance for mixtures of the four elements containing uranium were determined. Ten mg of U/ml was chosen as typlcal of actual sample solutions. Figures 1-4 also show the effect of adding U to the mixture of the four elements and to each individual pure element. In each case the addition of 10 mg U/ml re252
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C O N C E N T R A T I O N (ppiii,
50
Figure 4. for Rh
RIi)
Effect of Mo, Ru, Pd, and U on absorbance values
sulted in an increase in sensitivity. The absorbances of mixed standards containing U were, in every case, essentially the same as those of corresponding mixtures of the pure standards with uranium added. Regression curves of the form, C = a bA cA*, where C is concentration in ppm and A is absorbance, were found to provide the best fit of the data for each of the pure elements in 0.1N HCl solutions containing 10 mg U/ml. Standard errors = dBd,')n) for Mo, Ru, and Pd were of the estimates (Sppm on the order of +0.06-0.07 ppm and k0.12 for Rh. Standard errors resulting from imposing a linear relationship between absorbance and concentration were much greater. A series of mixtures containing 10 mg U/ml were prepared representing broad variations in the ratio of relative concen-
+
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Table I. Absorbance in Binary Combinations of Mo, Ru, Pd, and Rh Ratio of absorbance value in mixture to absorbance of Element corresponding determined, Element added, element in 20 PPm 20 ppm pure standard Mo Ru 1.1 Mo Mo Ru RU
Ru Pd Pd
Pd Rh
Rh Rh
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Pd Rh Mo Ru Rh Mo Ru
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1 .o 1 .o 0.58 1.5 1.3 0.98 0.67 0.81 0.30 0.28 0.45
Table II. Recovery of Molybdenum, Ruthenium, Palladium, and Rhodium from Pure Standards and from Mixtures Containing 10 mg of Uranium per ml Added 10.0 10.0 20.0 20.0 30.0 30.0 40.0 40.0 50.0 50.0
Mo, ppm Recovered 10.0 9.9 19.8 19.9 30.3 30.0 40.2 39.8 50.4 50.6
Added 20.0 50.0 30.0 10.0
40.0 20.0 50.0 30.0 10.0 40.0
Ru, ppm Recovered 20.6 50.0 29.3 10.0
39.3 19.3 49.1 30.1 9.6 39.4
Added 30.0
40.0 40.0 50.0 50.0 10.0 10.0
20.0 20.0 30.0
Table 111. Results of Analysis-Fissium Concentration4 of diluted sample aliquot sample by wt.) 0.6 0.6 0.3 0.3 0.12 0.12 0.06 0.06 1 .o 1.0
Pd, ppm Recovered 29.9 40.0 40.0 50.3 49.5 9.8 9.9 19.9 19.8 30.0
Rh,PPm Recovered 39.2 30.3 49.7 40.1 10.0 50.7 19.9 10.0 29.5 20.0 ~
Added 40.0 30.0 50.0
40.0 10.0 50.0 20.0 10.0 30.0 20.0
Alloy
z)*
Sample composition (wt. Ru Pd Rh ... ... 0.200 ... ... ... 0.194 ... ... 0.190 0 : is1 1 2 ... ... 0.191 0.294 2.51 1.96 1 ... 0.291 2.54 1.97 2 ... 0.295 2.53 2.00 1 ... 2 2.53 2.04 ... ... ... ... 0.190 0.282 AI 3 4 *.. ... 0.190 0.287 3e 1.0 ... ... 0,192 0.295 4" ... .*. 0.190 0.287 1.o 3 2.52 2.03 0.193 0.298 0.1 4 2.57 2.04 0.187 0.296 0.1 3d 0.1 2.53 2.07 ... ... 4d 0.1 2.04 2.50 ... ... 38 2.56 0.192 0.300 0.1-1 2.07 48 0.1-1 2.58 2.00 0.186 0.282 Initial ANL sample solutions contained -3 grams of sample per 100 ml of solution. Initial AI sample solution contained ~4 grams of sample per 100 ml. Analyses were made only at appropriate concentrations for each element. Aliquots evaporated nearly to dryness prior to dilution with water. Final solution contained 10 mg of added U per ml. e Each value is the average of 3 analyses of aliquots spiked with known amounts of the metals. Sample designation ANL 1 2
(z
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(I
trations of the four elements involved. Table I1 shows the composition of these mixtures and the corresponding recovery data. These data show clearly that the method is applicable over a broad range of compositions not necessarily limited to typical fissium alloys. It should be noted that all recovery data resulting from studies of mutual interference and other experimental parameters were obtained over a period of several months and were calculated from the standard regression curves of the form noted above. Statistically all data obtained over an extended time period can be treated as an individual set if an overall precision on the order of 3-5 % relative is acceptable. For more accurate work, however, standards and samples must be analyzed at the same time to obtain one statistical set. The composition of fissium alloy is such that it is desirable to determine Mo and Ru in a 0.1 sample solution (to eliminate the need for adding uranium to the sample solution) and Pd and Rh in a 1 % solution. It should be noted that in a 1 solution Mo and Ru concentrations would range between 200-300 ppm. Therefore, it was necessary to determine the effect of high concentrations of Mo and Ru on the determination of Pd and Rh. The effects of the variation in acid com-
position and concentration as well as the effect of the presence of Nb and Zr are also useful information. The effect of uranium at concentrations from 1-30 mg/ml on the absorbance of Mo, Ru, Pd, and Rh was studied over a range of concentrations from 10-100 ppm. The method was found suitable over the broader concentration range and absorbance values for all four elements showed no significant variation as a function of uranium concentration between 1 and 15 mg U/ml. However, at uranium concentrations of 30 mg/ml Mo absorbance values were reduced about 8 % ; Ru, Pd, and Rh absorbances were lower by 1-2%. No studies were made at uranium concentrations below 1 mg/ml. The presence of 300 ppm each of Mo and Ru in solutions containing 10 ml U/ml did not affect the absorbance values for Pd and Rh. Variations in HC1 and H N 0 3 concentrations up to 1.ON and H F up to 0.5Nsimilarly had no effect on the recovery of Mo, Ru, Pd, and Rh as long as uranium was present. The presence of 50 ppm each of Zr and Nb in standard solutions containing uranium caused no detectable interference. In all cases, except as noted, recoveries averaged better than k2.5%. Four samples, each weighing approximately 3-4 grams, VOL. 41, NO. 2, FEBRUARY 1969
253
from a single batch of fissium alloy were analyzed by atomic absorption. Two of these samples were analyzed at Atomics International and treated as described under the section on sample preparation. The other two samples were analyzed at Argonne National Laboratory, Idaho Falls, Idaho, by a similar technique using a Jarrel-Ash instrument (16). The data are summarized in Table 111. Both laboratories made several dilutions from the original sample solution. Mo and Ru are best determined in solutions containing approximately 0.1 % sample by weight; Pd and Rh are determined in solution containing about 1 % sample. Several analyses were performed on each sample at different concentrations simply to confirm earlier statements that the method was applicable over broad ranges of concentration and uranium content. Two sample aliquots were evaporated nearly to dryness and diluted to volume with water in order to determine whether all sample components would remain in solution and to provide solutions containing less acid. Additional uranium was added to a pair of 0.1% (sample by wt) sample solution as additional verification of the observation that uranium concentration below 30 mg/ml was not critical to the analysis. Other sample aliquots were spiked with known quantities of each element and analyzed simply as additional confirmation of the results. The results of the analyses performed at the two sites were in good agreement. No significant differences were apparent due to differences in the handling of sample aliquots. The role of uranium in eliminating interferences among the (16) Earl R. Ebersole, Argonne National Laboratory, Idaho Facilities, private communication, December 1967.
elements of concern here is not clear. The observed interferences are real, and, although variations in instrumental parameters, including flame conditions, influenced the shape of the absorption curves, the interferences as noted remained. Similarly no significant differences were observed in the results obtained with the single slot, premix burner and the 3slot burner except in stability. Since the ionization potentials for Mo, Ru, Pd, and Rh are relatively high, it is not likely that the ionization of these elements in the flame is a significant factor (affected by uranium) which acts to reduce sensitivity or which plays a role in mutual interference. It is more likely that the presence of uranium atoms or complex ions in the flames or in solution serves to stabilize the atom populations of these elements by breaking down or by preventing the formation of stable complex metal-halide ions of Mo, Ru, Pd, and Rh. It is also reasonable 40 suggest that the analysis of other alloys involving one or more of the elements, Mo, Ru, Pd, or Rh may be simplified or improved by the addition of uranium to sample matrices. ACKNOWLEDGMENT
The author is grateful for the kind cooperation of Earle R. Ebersole, ANL, in providing samples of fissium alloy for this work and to the Argonne National Laboratory for the effort expended in performing comparative analyses. RECEIVED for review August 7, 1968. Accepted October 18, 1968. Work supported by the United States Atomic Energy Commission.
Determination of Oxygen-to-Uranium Ratios in Hypo- and Hyperstoichiometric Uranium Dioxide and Tungsten-Uranium Dioxide E. A. Schaefer and J. 0 . Hibbits General Electric Company, Nuclear Systems Programs, Cincinnati, Ohio 45215 Several methods for the determination of oxygen-touranium ratios in hypo- and hyperstoichiometric UOz have been developed and/or evaluated, using NBS 950a (UaOs) and uranium metal as standards. these methods include (a) oxidation to U308+y,(b) a nitric acid dissolution procedure, followed by oxidation to UaOs+N,(c) an oxidation-reduction procedure, whereby the sample is first oxidized (in case the material is hypostoichiometric), then reduced to UOz.oo,(d) direct reduction with hydrogen (of hyperstoichiometric UOz) to UOz.oo, and (e) hydriding, whereby the free uranium metal in hypostoichiometric UOz is first converted to UH, and the hydrogen subsequently determined. I n addition, moisture has been determined on a number of samples in order to evaluate its effect on the oxygen-to-uranium ratios obtained using the above methods. In general, the accuracies obtained are within the expected accuracies of the procedures used. Where applicable, the above methods have been applied to W-UOz*x samples, using UOz control specimens to evaluate the accuracy of the results obtained.
THEPURPOSE of this paper is to attempt to clarify the determination of oxygen-to-uranium (O/U) ratios in UOZ*, and W-UOz,, and, in addition, to present methods which have 254
ANALYTICAL CHEMISTRY
been developed and evaluated for these determinations. It is all too frequently assumed that the determination of an O/U ratio in UOz*, can be easily made by ignition of the sample to u3os and calculating the O/Uratio on the basis of weight change. This result can be in error because it neglects the effect of adsorbed moisture if present, and some samples attain different final weights depending on the technique used for oxidation. For example, our oxidation technique involves a preliminary oxidation of 470 "C for a minimum of 4 hours followed by 4 hours at 900 "C. On a number of samples that we have analyzed, results are 0.01 O/U unit too high if the 470 "C preliminary oxidation is omitted. Other samples did not reach a maximum weight at 900 "C even after oxidation for 72 hours. Inasmuch as a number of fuel element core materials are being investigated under conditions which could lead to the formation of nonstoichiometric uranium dioxide, it is important that methods be available for accurately measuring oxygen-to-uranium ratios. Depending on the temperature, hypostoichiometric material could contain uranium metal which could be highly reactive with other materials present. On the other hand, hyperstoichiometric material at elevated
