A Critical Study of Carbon-Reduction Techniques for the Determination of Oxygen in Thorium and Yttrium Metals VELMER A. FASSEL, WAYNE E. DALLMANN, and C. CLIFTON HILL Institute for Atomic Research and Department o f Chemistry, Iowa State University, Ames, Iowa
b A critical study on the determination of the oxygen content in thorium and yttrium metals by carrier-gas fusion, vacuum fusion, and d.c. carbonarc extraction methods has delineated the experimental conditions under which quantitative accuracy can b e achieved. Synthetic metal-oxygen standards were employed to validate the absolute accuracy.
T
are included among the many metals whose physical and mechanical properties are influenced by the presence of trace quantities of interstitial oxygen (’7, 21 , 23, 28). I n order to appraise these effects, accurate analytical determinations of the oxygen contents of these metals are required. Sloman and Harvey (24) have shown that the oxygen in pure thorium oxide is quantitatively reduced to carbon monoxide when the oxide is fused in a carbon-containing, iron reaction medium maintained a t 1900° C. under a high vacuum. Under similar environmental conditions, these investigators (24) also determined the oxygen contents of a series of powdered thorium metal specimens. KO validation on the accuracy of the determinations was given. Booth, Bryant, and Parker (4) employed a platinum reaction medium a t 1900’ C. in a microvacuum fusion facility, and obtained analytical results on two thorium specimens which were in accord with iron-bath values reported by Sloman. Smiley (26) employed the platinum reaction medium a t 1800’ C. under a flow of inert carrier gas to determine the oxygen content of a thorium metal specimen. N o accuracy validation was reported. Banks, O’Laughlin, and Kamin ( 2 ) employed the carrier-gas fusion technique for the determination of oxygen in yttrium. The metal samples were fused a t 2100’-2200’ C. in a platinum reaction medium which was provided by adding three times the sample weight of platinum to the crucible along with the yttrium specimen. Good agreement was reported between the analytical results obtained by this procedure and those obtained by a platinum bath, vacuum-fusion procedure employed by us a t that time. Emission spectroHORIUM AKD YTTRIUM
graphic results also showed concordance ( d ) , which would be expected since the spectrographic calibrations were based on vacuum-fusion-analyzed standard samples. Although concordance of the results obtained by Sloman and Harvey and by Booth and coworkers on oxygen in thorium, and by Banks et al. on oxygen in yttrium, strongly suggests that absolute analytical accuracy was also represented, it is appropriate to emphasize that both the accuracy and precision of the vacuum and the carriergas-fusion techniques are sensitively dependent on the environmental conditions prevailing in the crucible. The data reported in this communication indicate that the absolute accuracy of the oxygen results obtained under the experimental conditions used by Sloman and Harvey (24) and by Smiley (26) for thorium, and by Banks et al. (2)for yttrium, should be viewed with reservations unless quantitative recovery is demonstrated with the particular apparatus employed. Furthermore, the data presented in this paper demonstrate that a considerable improvement in precision can be achieved by utilizing certain variations in the reaction medium. The analytical accuracy of the determination depends on whether the fusion conditions employed provide the following : a suitable carbon-containing reaction medium so that the carbon reduction reaction proceeds quantitatively; temperatures sufficient to effect the carbon-reduction reaction; and, some means for minimizing vaporizationgettering effects so that the carbon monoxide evolved can be quantitatively recovered. The experimental approach used by us in validating the absolute accuracy of determinations of oxygen in a metal is to study the basic carbon-reduction reaction under markedly different environmental and thermodynamic conditions. If experimental conditions are found which lead to maximal recoveries and concordance of the analytical results, a high degree of confidence can then be placed on the accuracy of the determinations. Validation of the absolute accuracy is then provided if quantitative oxygen recoveries can be realized when synthetic standard samples are analyzed under these conditions. ‘The results of such a
definitive study on the determination of oxygen in thorium and yttrium by the vacuum fusion, carrier-gas fusion, and d.c. carbon-arc techniques are presented in this paper. A discussion on the basic environmental and thermodynamic differences among these techniques was presented in an earlier communication (9)
9
EXPERIMENTAL
Preparation of Synthetic Standards. Synthetic standard samples of thorium-oxygen and of yttrium-oxygen were prepared in the following manner. A “master alloy” was prepared by drilling several small holes into a large button of low-oxygen content base-metal, and packing the cavities with known amounts of the degassed, high-purity base-metal oxide. Tapered plugs of the base-metal were then fitted into the cavity openings and the contained oxide was further degassed by application of a low-current arc in an argon atmosphere. The oxide-metal composite was then arc-melted in an atmosphere of purified argon, and was flipped nine times, thus resulting in a master alloy containing a known, homogeneous oxygen distribution. I n the same manner, lower concentration standards were prepared by successive dilutions of the master alloy with known amounts of the base metal. Furnace-Fusion
Reaction Media.
I n the historical development and refinement of the vacuum fusion and carrier-gas-fusion techniques, a variety of alloying metals have been employed to provide reaction media in which the carbon-reduction reaction proceeded rapidly and quantitatively. Using previously published information and our own experiences on the determination of oxygen in similar metals as a guide, we selected the following reaction media for intensive study: the iron-bath procedure of Sloman and Harvey (24) (for thorium only) ; variations of the platinum-bath procedure (9, 16); the platinum-flux procedure of Banks et al. ( 2 ) (for yttrium only); and variations of the platinum-tin-bath procedure (18, 20). The vacuum-fusion operating conditions for the iron bath procedure were patterned after those given by Sloman and Harvey (24). At the extraction temperature, 1900’ C., the iron melt rapidly became viscous and only a few samples could be analyzed before sample dissolution in the melt became very VOL. 38,
NO. 3, MARCH 1966
421
Table 1. Experimental Conditions for Determination of Oxygen in Thorium and Yttrium b v Vacuum-Fusion Technique
Vacuum fusion, gas-analysis unit, NRC Equipment Corp., Model 9125
Analysis facility
(16, 32).
422
Guldner
- Reach
furnace Ultra Carbon Corp., C-625 gra hite crucible and E)-703 graphite funnel floated in -200-mesh UCPS graphite powder in a quartz thimble suspended by platinum wire hooks within aircooled borosilicate glass jacket. Lepel High Frequency Furnace Corn.. induction heater. heater Mead T-2.5B, 2'/2-kw: output, 450-kc. nominal frequency. Conventional low-pressure Analytical oxidation and selective system absorption and condensation separation (SB). Crucible temperature Apparatus raised to 2400" C. over degassing 1-hour period and maintained at this temperature until the pressure level was less than Torr. Platinum bath procedure, Bath for thorium only; not degassing less than 20 or more than 60 grams of 1.2gage platinum wire added to the crucible at 1700" C. and degassed at 1950" C. until pressure level was less than 10-6 Torr. Platinum-tin bath procedure, for both thorium and yttrium; not less than 20 or more than 40 grams of a composite 80(P t ) : 20(Sn) bath added intermittently to the crucible at 1400" Cd and degassed at 1700 C. until pressure level was less than Torr. 0.3-0.5 gram thorium or Bath yttrium added to the conditioner degassed bath. Furnace 2-4 fig. oxygen, for extraction temperature blank and time given below. Platinum bath procedure, Extraction for thorium only; 1950" temperaC. Platinum-tin bath ture procedure, for both thorium and yttrium; 1700' C. 15-30 minutes. Extraction time Samples and Carefully filed and cleaned specimens weighing 0.1flux 0.5 gram fluxed with 0.5 gram of 12-gage platinum wire, all encased in a 0.35 gram platinum capsule. Platinum flux 8-10 rg. oxygen gram-' of platinum blank Maximum Not to exceed 10 wt. % thorium or yttrium in solute metal conbath. centration
Crucible assembly
(13).
ANALYTICAL CHEMISTRY
sluggish. The data presented later show that quantitative recovery of oxygen from typical thorium samples and from synthetic thorium-oxygen standards was not achieved with this reaction medium. Preliminary factorial studies on variations of the platinum bath, vacuum fusion procedure revealed that maximal oxygen recovery from thorium and from yttrium were obtained under the following conditions : [All temperatures reported in this paper were measured with an optical pyrometer (Pyrometer Instrument Co., Bergenfield, iY, J., Catalog No. 85) calibrated in accordance with the instructions provided by the manufacturer.] extraction temperature of 1900' C. for yttrium and 1950' C. for thorium; preconditioning of the platinum bath with 0.3-0.5 gram of the particular solute metal; simultaneous addition of platinum along with the sample; and, maintenance of the solute metal concentration in the fusion melt a t less than 10 weight per cent. Similar carrier-gas fusion studies on thorium revealed that maximal oxygen recovery was obtained under the same conditions, except that a fusion temperature of 2500' C. was required. The carrier-gas-fusion operating conditions for the platinum flux procedure were similar to those described by Banks et al. ( 2 ) . Under these conditions, maximal extraction of oxygen from yttrium was not achieved. If the temperature cycling described by Banks et al. (8) was omitted and the crucible temperature was maintained at 2100-2200' C. during the entire fusion period, maximal oxygen recoveries were obtained. However, the data presented later demonstrate that even under the prolonged fusion a t operating temperatures, the oxygen recoveries were not quantitative. Preliminary vacuum and carrier-gas fusion studies with variations of the platinum-tin reaction medium showed 0.140
0.1 20
I
I
that maximal recoveries on both thorium and yttrium were realized when a weight per cent bath composition of 80(Pt) :20(Sn) was properly employed. Cnder vacuum fusion conditions, care was required during the preparation of the composite bath in order to minimize spattering when a sample contacted the melt. Small portions of the platinum and tin were slowly and intermittently added to the crucible a t 1400' C., followed by degassing a t the operating temperature. Other pertinent experimental conditions delineated by the factorial studies were as follows: extraction temperature of 1700' C. and 2300' C., respectively, for vacuum fusion and carrier-gas fusion, for both thorium and yttrium; preconditioning of this composite bath with 0.3-0.5 gram of the particular solute metal, which was added to the degassed melt a t 1400' C. and 1700' C., respectively, for vacuum fusion and carrier-gas fusion; simultaneous addition of platinum along with each sample, plus 0.1 gram of tin for the carrier-gas fusion samples; and, maintenance of the solute metal concentration in the fusion melt a t less than 10 weight per cent. D.C. Carbon-Arc Extraction. Since neither the emission spectrometric ( 1 1 ) nor the gas-chromatographic (SO) modifications of the technique, as presently practiced, are based on absolute measurements of oxygen concentrations, it has been necessary t o resort to standard samples for calibration purposes. If a series of furnace-fusion analyzed standard samples are used as calibrating standards for a particular metal, any systematic analytical error in the fusion procedures mould be reflected in the resultant calibration as well. It has recently been observed that the spectrographic intensity ratios ( I O ) and gas-chromatographic peak heights (SO) obtained on a series of different metals scatter rather uni-
I I I THEORETICAL CALCULATED IPLATINUM-TIN BATH, 1700' C PLATINUM BATH, 1950'C IRON BATH, 1900,*C
I
I
ae
-
0.100
4
! i 0.080
K l-
5 0 z 0
0.060
0 2
w
Q040
x
0
O ' nO T SYNTHETIC STANDARDS SAMPLES Figure 1. Evaluation of reaction media for vacuum-fusion determination of oxygen in thorium
formly around single analytical curves. These "master" analytical curves therefore tend to erase any systematic errors in the reference, furnace-fusion values. The carbon-arc extraction results reported in this paper were obtained from such "master" curves.
Recommended Analytical Procedures. Tables I and I1 outline t h e
pertinent experimental conditions for t h e vacuum fusion and carrier-gas fusion determinations. Experimental details for t h e d.c. carbon-arc extraction, emission-spectrometric (10, 11) and gas-chromatographic (SO) methods were previously described. Sample preparations and other operational procedures followed standard practice. RESULTS A N D DISCUSSION
X summary of the data obtained on the synthetic thorium-oxygen standards and on typical thorium metal samples is found in Table 111. +4high degree of concordance is apparent among all of the analytical results including agreement between the calculated oxygen contents of the synthetic standards and the contents measured by the four techniques under different environmental conditions. These data therefore provide strong experimental verification on the quantitative accuracy of each technique. The data for the platinum bath, vacuum-fusion procedure also lends support to the absolute accuracy of the results previously reported by Booth et al. (4). It is relevant to note that for both fumace-fusion techniques, the platinum-tin bath variation possesses a distinctive advantage over the pure platinum bath-Le., quantitative recovery can be achieved at operating temperatures lower by approximately 200' C. A comparison of part of the data in Table I11 with results obtained with the iron reaction medium is shown in Figure 1. It is evident t h a t the iron bath procedure did not provide quantitative oxygen recovery at 1900' C. Since the iron bath tended to solidify after only a few sample determinations, a n intensive study of this reaction medium was not undertaken. Under carrier-gas-fusion conditions, the platinum bath procedure at 1800' C. consistently yielded analytical results at least 15% lower than those recorded in Table 111. Therefore the absolute validity of oxygen results obtained under the conditions described by Sloman and Harvey (24) and by Smiley (26), should be viewed with reservations, unless quantitative recovery can be demonstrated with the particular arrangement employed. A summary of the analytical results on typical yttrium samples and on the synthetic yttrium-oxygen standards is found in Table IV and Figure 2. These data, as well as those for thorium in Table 111, are the averages of at least three determinations, consequently small but consistent differences in
Table
II. Experimental Conditions for Determination of Oxygen in Thorium and Yttrium by Carrier-Gas-Fusion Technique
Analysis facility
Trap calibration Calibration Standard solutions of poverification tassium acid phthalate transferred with microsyringe into tin capsules. The solutions are slowly evaporated to dryness at temperatures below 100' C. After sealing the open end of the capsule (by crimping), the capsules are flattened into a compact form (19). Briquets made from blends of powdered cupric oxide and graphite were also used. Carrier gas Argon, at flow rate of 100 ml. mine-' Purification Achieved by passing carof argon rier - gas through a Schutze reagent - Ascarite - Anhydrone column, followed by titanium sponge metal heated to 600' C. Apparatus Crucible raised to maxidegassing mum temperature Over 1-hour Deriod and maintained at this temperature until acceptable blanks obtained. Bath Platinum bath procedure, for thorium only; 5-10 degassing
grams of 12-gauge platinum wire added to the crucible at 1700' Cd and degassed at 2500 C. for 30-45 minutes. Platinum-tin bath procedure, for both thorium and yttrium; 6-15 grams of a composite SO(Pt):20(Sn) bath added intermittently to the crucible at 1700' Cd and degassed a t 2300 C. for 30-45 minutes. Bath 0.3-0.5 gram thorium or conditioner yttrium added to the degassed bath. Furnace Platinum bath at 2500' blank C.; 5-8 pg. oxygen min.-' of trap time." Platinum-tin bath at 2300' C.; 2-4 pg. OXYgen min.-' of trap time. Reduction Platinum-bath procedure, temperafor thorium only; 2500' ture C. Platinum-tin bath procedure, for both thorium and yttrium; 2300' C. Reduction Platinum bath procedure, time for thorium only; 6 minutes with power on. Platinum-tin bath procedure, for both thorium and yttrium; 8 minutes with power on. Samples Varied in weight to restrict total oxygen liberated to 100-250 figb. Flux Platinum bath procedure; three times sample weight of platinum in contact wjth the thorium specimen. Plathum-tin bath procedure; three times sample weight of platjnum plus 0.1 gram tin in contact with the thorjum or yttrium specimen. Platinum 8-10 pg. oxygen gram-' of flux blank PlatinLim. Maximum Not to exceed 10 weight solute per cent thorium -or metal conyttrium in bath. centration a Because of the high reduction temperature, a furnace blank was taken every two analyses. Total oxygen quantities exceeding 250 pg. resulted in low recovery (9, 14).
the average results are significant. A close examination of the data in Table IV reveals t h a t there are systematic, though small, differences among the data. Considering first the carrier-gas fusion results, the platinum- tin bath data are consistently higher than the values obtained under the environmental conditions recommended by Banks et al. (2). Moreover, the oxygen recoveries on the synthetic standards obtained by the platinum-tin bath environment are in accord with the calculated values, whereas the platinum flux results are consistently low. These data suggest that the absolute accuracy
of the analytical results obtained by the platinum flux procedure given by Banks et al. (2) should also be viewed with reservations, unless quantitative recovery is demonstrated with the particular apparatus employed. I n addition to the ability of the platinum-tin bath to achieve quantitative extraction at lower temperatures, another benefit of the platinum-tin environment is shown by the graphical plot of the data in Figure 2A. It is apparent that the precision of observations on the synthetic standards, which are presumed to be more homogeneous than the typical samples, is markedly better than the
Crucible assembly
Analytical system
Laboratory Equipment Corp. (LECO), high-frequency induction furnace, Model 537, 4.5kw., 3-Mc. nominal frequency. Crucible thimble, LECO 534-315. Carbon black packing, LECO 501-92. Gra hite crucible, Ultra Cargon Corp., C-625, machined to length of 2,1/s inches, with beveled rim. Capillary trap-manometer system modified from Smiley's design (26) so as to consist of a dual spiral - trap assembly similar to that described by Hanin ( 1 4 ) . Oxidation of carbon monoxide to carbon dioxide accomplished with modified (26) Schutze reagent (88). Procedure of Smiley (86).
VOL. 38, NO. 3, MARCH 1966
423
-
I
0.500
)A) CARRIER-GAS
-d-
I
I
I
1 -
-
FUSION
I-
1
/
ff-, f
_. 8 0.100
I Pt FLUX (2100-2200'C)
-$ Q
0 Pt-Sn BATH; Pt-Sn FLUX (2300'C)
0.050
P pP
G
E zW 0.500
(B) VACUUM FUSION
0
0
i
z W c3
>
X 0
e+->
I Pt BATH; Pt FLUX (1900 'C)
-
VALUE
O.O5'
4-
"-e
0 Pt-Sn BATH; Pt FLUX (1700oC)
4-
-
SYNTHETIC STANDARDS: 2,4,7, 8, IO
-
T Y PICA L SAM P LESI,: 3, 5, 6,9,11, 12, 13
--
+f@
I
corresponding results for the pure platinum reaction medium. Virtually this same pattern of behavior is observed in Figure 2B for the data obtained under vacuum fusion conditions, although the difference in recovery and precision in several instances either does not exist or is not significant. The data presented above clearly show that the platinum-tin bath possesses distinctive advantages for the furnace-
Table 111.
Comparative Analytical Data on Determination of Oxygen in Thorium
Absolute synthetic standards, wt. % oxygen 0.19 0.12 0.070 0.040 0.020 Samples
Carrier-gas fusion, wt. 70oxygen Pt bath Pt-Sn bath 2300" C. 2500" C. 0.19 ... 0.12 0.12 0.073 0.067 0.038 0.038 0.020 0.020 0.14 0.11 0.040 0.036 0.025 0.024 0.018
8
424
fusion determination of oxygen in metals. These observations confirm earlier scattered reports on the beneficial aspects of tin additions to the fusion media. Booth and Parker ( 5 ) , using a microvacuum fusion apparatus, found that satisfactory dissolution of beryllium in the platinum melt was not achieved unless tin ryas added to the melt both before the addition of any samples and together with each sample.
0.011
0.13 0.11 0 : 037 0.025
.*. ... ...
ANALYTICAL CHEMISTRY
Vacuum fusion, wt. 70oxygen Pt bath Pt-Sn bath 1700" C. 1950" C. 0.19 ... 0.12 0.12 0.070 0.074 0.042 0.042 0.021 0.021 0.13 0.11 0.042 0.033 0.026 0.023 0,019 0,010
0.14 0.11 0 033 0.025
D.C. carbon-arc, wt. % oxygen FpectroGas chrographic matographic ... 0.19 0.12 0.12 0.064 0.068 0.038 0.042 0.020 0.020 0.13 0.11 0.042 0.037 0.029 0.025
0.16 0.11 0.042 0.033 0.026 0: 021 0,010
These same investigators later reported that results on oxygen in beryllium remained significantly lower and were more erratic when the tin was omitted (6). Everett and Thompson's (8) extensive observations on the gettering of carbon monoxide during the determination of oxygen in beryllium clearly showed that addition of tin with the sample caused a marked reduction in loss of the evolved gas. Wood and Oliver ( S I ) observed that oxygen could be quantitatively determined in titanium-manganese alloys only by adding tin with the sample to the platinum melt a t 1500' C., allowing the manganese to vaporize, and then increasing the temperature to effect the carbon reduction reaction. McKinley (18) demonstrated that accurate and precise determinations of oxygen in chromium could be obtained using a n 80(Pt): 20(Sn) bath at 1650' C. Accurate determinations could not be achieved with baths previously used, namely, iron, iron-tin and platinum. Finally, in the last several years, an 80(Pt) :20(Sn) bath composition has been receiving increasing attention by participants in various cooperative analytical programs (12, 20) as a desirable reaction medium for the determination of oxygen in refractory metals. Although much of the tin remains alloyed in the fusion bath (ZO), some of it vaporizes and then recondenses on cooler parts of the furnace assembly. Therefore, the tin may have important roles in the liquid, vapor, and condensed states (18). However, the actual operational functions of the tin which are conducive to greater and more reproducible oxygen recovery still appear uncertain. Among the functions which have been attributed to the tin are the following: lowering of the melting temperature of the bath (2O), (there is a lowmelting eutectic at the 72(Pt) : 28 (Sn composition) ; increasing the fluidity of the melt (12, 27), and initiating earlier surface reactions of the sample (8),thus facilitating reaction between dissolved carbon and the oxygen impurity; a sweeping action ( 1 ) similar to that of a diffusion pump, and a mechanical stirring action ( I $ ) , aiding in the removal of gases from the melt and suppressing vaporization of the more volatile sample constituents (8); and, minimizing various gettering processes, either by covering reactive metal surfaces formed by condensation on cooler parts of the furnace assembly (3, I 7 ) , or by reducing the efficiency of dispersal gettering (8, 29, S I ) . Very little unequivocal experimental evidence to support any of these mechanisms has been offered. There is, however, no doubt that the presence of tin in the reaction medium contributes to the more efficient and reproducible extraction of the oxygen content of thorium, yttrium, and
Table IV.
Absolute synthetic standards, wt. 7 0 oxygen 0.48 0.31 0.20
0.13 0.080 Samples 1
2 3 4
-.i
6 7 8
(16) Horrigan, V. &I., Fassel, V. A., Goetzinger, J. W., Zbid., 32, 787 (1960). (17) McDonald, R. S., Fagel, J. E., D.C. Ballis, E. W., Ibid., 27, 1632 (1955). carbon-arc, (18) McKinley, T. D., Pitt. Conf. on wt. % Anal. Chem. and Applied Spectroscopy, Vacuum fusion, oxygen Pittsburgh, Pa., March 1959. wt. oxygen Gas (19) McKinley, T. D. “Procedure for chromatoPt bath, Pt-Sn bath, Preparation of Absolute Oxygen Stand1700” C. graphic 1900” C. ard,]’private communication, 1959. 0.48 0.49 (20) Mallett, hl. W., Talanta 9, 133 0.45 0.31 (1962). 0.31 0.31 0.20 0.23 (21) hlilko, J. A., Adams, R. E., Harms, 0.20 W. O., in “The Metal Thorium,” Wil0.14 0.13 0.13 helm, H. A. ed., Chap. 13, American 0.080 0.079 0.083 Society for Metals, Cleveland, Ohio, 1958. 0.46 0.50 0.47 0.29 0.32 ... (22) Schutze, M. Ber. 77B, 484 (1944). 0.27 0.30 0.30 (23) Simmons, C. R., in “The Rare 0.25 0.26 0.23 Earths,” Spedding, F. H., and Daane, 0.12 0.13 0.11 A. H., ed., Chap. 18, Wiley, Kew York, 1961. 0.047 ... 0.047 (24) Sloman, H. A., Harvey, C. A., 0.039 0.040 ... Kubaschewski, O., J. Znst. Metals 0.038 0.036 ... 80, 391 (1951-52). (25) Smiley, W. G., Nucl. Sci. Abstr. 3, 391 (1949). (4) Booth, E., Bryant, F. J., Parker, A,, (26) Smiley, W. G., ANAL. CHEM.27, Analyst 82, 50 (1957). 1098 (1955). (5) Booth, E., Parker, A., Zbid., 83, 241 ( 2 7 ) Stanley, J. K., von Hoene, J., (1958). Weiner, G., Ibid., 23, 377 (1951). (6) Booth, E., Parker, A., Zbid., 84, 546 (28) Tucker, R. C., Gibson, E. D., Carl(1959). son, 0. N., Nucl. Metall. Series X, ( 7 ) Carlson, 0. N., Bare, D. W., Gibson, 315 (1964). E. D., Schmidt, F. A., in “Symposium (29) Turovtseva, Z. M.,Litvinova, N. F., on Newer Metals,” ASTN Spec. Tech. “Proceedings of the Second U. N. InterPubl. SO.272, pp. 144-159 (1959). national Conf. on Peaceful Uses of (8) Everett, &I. R., Thompson, G. E., Atomic Energy,” Vol. 28, pp. 593-603, Analyst 87, 515 (1962). United Xations, New York, 1958. (9) Fassel, T’. A., Dallmann, W. E., Winge, R. K., Fassel, V. A., ANAL. Skogerboe, R., Horrigan, T’. M., A N ~ L . (30) CHEM.37, 67 (1965). CHEM.34, 1364 (1962). (31) Wood, D. F., Oliver, J. A., Analyst (10) Fassel, I-. A., Goetzinger, J. W., 84, 436 (1959). Spectrochim. Acta 21, 289 (1965). (32) Yeaton, R. A., Vacuum 2, 115 (1952). (11) Fassel, T. A., Gordon, W. A., ANAL. CHEX.30, 179 (1958). (12) Guldner, W. G., Talanta8,191 (1961). (13) Guldner, W. G., Beach, A. L., AXAL.CHEW22, 366 (1950). RECEIVEDfor review October 29, 1965. (14) Hanin, &I., Rev. MBt. 57,1133 (1960). Accepted December 13, 1965. Con(15) Hansen, W. R., hlallett, hl. W., tribution No. 1822. Work performed in Trzeciak, hl. J., AXAL. CHEM. 31, the Ames Laboratory of the U. S. Atomic 1237 (1959)r Energy Commission.
Comparative Analytical Data on Determination of Oxygen in Yttrium
Carrier-gas fusion, wt. % oxygen Pt flux, Pt-Sn bath, 2100-2200’ C. 2300’ C. 0.46 0.48 0.29 0.32 0.18 0.20 0.11 0.13 0.069 0.081 0.4!3 0.30 0.27 0.22
n 12 .
~~
0.040
0.033 0.031
0.50 0.32 0.32 0.25 0.13 0.043 0.040 0.036
other metals, a t lower fusion temperatures than are required for a simple platinum bath. ACKNOWLEDGMENT
The authors are indebted to Royce
K. Winge and John W. Goetzinger for performing some of the analyses reported in Tables I11 and IV. LITERATURE CITED
(1) Albrecht, W. hl., hlallett, M. W., ANAL.CHEM.26,401 (1954). ( 2 ) Banks, C. T’,, O’Laughlin, J. W., Kamin. G. J.. Ibid.. 32. 1613 (1960). (31 I , Beach. A. ‘L.. duldner. JV’. G..’ in “Svmnosium on ‘Determination of Gases in “hI&als,” ASThl Spec. Tech. Publ. NO. 222, pp. 15-24 (1957).
Three-Wavelength X-Ray Absorption Edge Method for Determination of Plutonium in Nitrate Media E. A. HAKKILA, R. G. HURLEY, and G. R. WATERBURY University of California, 10s Alamos Scientific laboratory, 10s Alarnos, N.
b A new x-ray absorption edge method was developed for determining plutonium in nitrate solutions, In this method the transmitted x-ray intensities a t three wavelengths are measured. The KP x-ray for niobium and the K a x-rays for molybdenum and niobium are produced by irradiating a niobium-molybdenum secondary target with x-rays from a tungstentarget x-ray tube, and the intensities of these x-rays are measured after passing through an absorption cell filled successively with water and a solution of known plutonium content. Then the reduction in the transmitted intensities of the KP x-ray for niobium
M.
and the K a x-ray for molybdenum, which bracket the L 111 absorption edge for plutonium, are measured through the same cell filled with the sample solution. The absorption of these x-rays is related to plutonium concentration using accepted absorption principles. The method is applicable to the determination of plutonium concentrations of 10 to 25 mg. per ml. with a relative standard deviation of approximately O.6Y0.
A
method for determining plutonium in nitric acid solutions was needed to supplement potentiometric titration and radiochemical RAPID
methods for plutonium assay (3). The main requirements of the method were that it have a relative standard deviation no greater than 0.5% and produce results within 4 hours of receipt of sample. X-ray absorption edge methods, which provide the required speed and precision, have been applied to the determination of numerous elements, including plutonium ( 2 ), that have x-ray absorption edges in the 0.5- to 2-A. wavelength region. However, the conventional x-ray absorption edge method, in which measurements are made a t two wavelengths ( I ) , does not lend itself to reliable analysis of materials contaminated only with impurities that VOL. 38, NO. 3, MARCH 1966
425
